backpack. the other man is wearing a black baseball cap with white bands on the bill and a white letter on the front. he's wearing a white v-neck t-shirt, beige pants, a black hooded coat. he's carrying a dark backpack. this video shows the men walking together toward the finish line. the fbi says the man in the white baseball cap first attracted their attention because he appeared to be placing one of the bombs. >> the only one observed to be planting what we believe is the device is suspect number two with the white cap. >> what time did they put the devices down? >> i don't have the precise time in front of me. it was shortly before the bomb blasts went off. >> reporter: investigators say their attention was focused on the man with the white hat. as they analyzed more pictures they realized the two spent time together. they say they did not see the other man actually planting a bomb. >> somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects.

it may be difficult but the nation is counting on those with information to come forward and provide it to us. >> reporter: as for the bombs themselves investigators believe both were likely detonated by electronic remote controls. federal agents have been canvassing hobby stores in the boston area asking about recent purchases of remote-controlled devices. the fbi's hope is that people will search their memories to see if they can shed light on what's now the most important question. who are these two men? brian? >> so, pete, the video and stills have only been in our hands for about an hour now. looking at it, what can we glean from physical evidence, possible relationship between the two men? i have looked at the web tonight. there is already a slew of theories as to what the iconography is on both hats. leading theory is it's a bridgestone golf logo on the darker of the two. what can be learned? >> reporter: as for the bridgestone logo, that's what we

are told by federal investigators who have seen these pictures for a while based on their own analysis. one thing the fbi said tonight is that this is in essence a starter set of photos. they hope to keep looking through the pictures and as they come up with pictures that show perhaps better views and better resolution, they will release those, too. this isn't it. they hope to have more. >> after all the talk about all the good digital images of the finish line, the video that's been released is so far pretty standard surveillance camera, building-mounted. >> reporter: right. highest quality in one sense and also a bird's eye view. because the people who are on the ground, their visibility is going to be limited as the crowd in front of them blocks their view. secondly, it's the surveillance camera that gives them the strategic look at what these men were doing. it's motion video so they can watch their movements. >> all right. pete williams in our washington newsroom. no doubt a big step forward in this investigation. lester holt was on the street in boston when the photos went

public at that very moment. he witnessed the start of what someone today called the first nationwide electronic crowd-sourced manhunt of the digital era. lester, good evening. >> reporter: brian, good evening. when the crowd watching us glommed onto the fact we were talking about pictures of suspects, the smartphones immediately came out. people started watching that video. one man said to me, i wish i knew them. the president was here just a few hours before we learned of the suspect. whether he knew about them or not is unclear. he had a message for whoever did this. we will find you. bostonians stood for hours in a line ten blocks long for a chance to publically share their sorrow and even their fears. >> i'm sickened by this. we live in such a free country and to have a sense of

insecurity. ♪ >> reporter: inside the cathedral, tears flowed openly. >> we will rise in community. >> reporter: in what has become a ritual of large scale american tragedies, families and first responders along with civic leaders and the general public turn to faith and each other to work through pain. >> tomorrow the sun will rise over boston. >> reporter: president obama in an all too familiar role of comforter-in-chief drew lessons from the marathon itself. >> scripture tells us to run with endurance the race that is set before us. >> reporter: the president also paid tribute to those who died. >> we come together to pray and mourn. >> reporter: in remarks laced with resolve in the face of an unknown enemy the president rallied boston and america to be undeterred. >> the world will return to this great american city to run harder than ever and to cheer

even louder for that 118th boston marathon. >> reporter: as the crowd applauded and cheered, the president wiped away tears. later, he met with race volunteers to thank them. as boston tends to its emotional wounds, six people injured in the bombings remain in critical condition. the number still hospitalized, fewer than 60. >> in general, patients are getting better. we are happy with their progress. >> reporter: meantime, the beefed-up police presence in boston was ramped up even more for today's presidential visit. a reminder that this attack remains unsolved. first lady michelle obama traveled with the president today and visited patients and staff at some of the hospitals that treated the wounded. brian? >> lester holt in boston for us tonight. lester, thanks. we shift our attention now out west to the huge concussion and fire that tore through the town of west texas last night. a massive explosion at a

fertilizer supply outlet. west is about 20 miles north of waco. it only covers a couple dozen blocks but after the blast which actually registered a 2.1 on the richter scale, a big part of the community is simply gone today. while it is unclear as of now how many people have been killed the mayor says 30 to 40 people are missing. a lot of those first responders. 160 more are injured. nbc's miguel almaguer is at the scene for us tonight. miguel, good evening. >> reporter: brian, good evening. that explosion took place a mile away from here. we have been asked to keep our distance as rescue teams search for the missing. it's feared at least 15 are dead. as you mentioned, 160 wounded. officials worry both those numbers may climb. the blast decimated four city blocks. a war zone where tonight first responders are searching for survivors. in the small town of west --

>> firefighters down. again, there has been an explosion. there are firefighters down. >> reporter: -- emergency crews scoured debris for their own. west volunteer firefighters who rushed in, but never made it out. >> this tragedy has most likely hit every family. it's touched practically everyone in that town. >> reporter: the fire at the west fertilizer company broke out wednesday evening. minutes later, a deadly explosion. >> are you okay? >> dad? i can't hear. >> cover your ears. >> i can't hear. >> reporter: the blast so powerful it was felt 50 miles away and registered as a 2.1 seismic event. >> the windows came in on me. the roof came in on me. the ceiling came in. i worked my way out to go get some more help. >> reporter: outside of waco, the west fertilizer company sits adjacent to a nursing home, two schools and an apartment complex. tonight the area is in shambles. roofs peeled back, walls ripped apart.

some 80 homes gone. fears of a toxic cloud forced a makeshift triage center at a nearby football field to be moved wednesday. today, officials deemed the air safe while defending firefighters who used water to battle the ammonia-fuelled blaze. >> i don't think we should be second guessing right now the actions of the first responders and whether they were applying water at the appropriate place at the appropriate time. >> reporter: texas has seen disaster before. in 1947, nearly 600 were killed when a ship carrying ammonium nitrate exploded. it's the same material used by timothy mcveigh in the 1995 oklahoma city bombing. >> we need every ambulance we can get. we got a lot of firemen down. >> reporter: in west, police say so far no signs of foul play. but heartbreak here is everywhere. >> i'm kind of numb. really don't know. like i said, it will probably hit me at the funeral. my family is taking it really bad. really bad right now.

it's really rough. >> reporter: as the search for the missing presses on. >> it's one of those that helps everybody. wants to help everybody in need. >> reporter: as federal and local officials investigate we should note that in 2006 the west fertilizer facility was fined for not obtaining or having a permit. they have since rectified the problem. tonight it is believed 40 people are injured and still in the hospital. brian, we have learned tonight that one of the men who was killed was an off-duty dallas firefighter who came here to help. brian? >> miguel almaguer in the badly shaken town of west texas tonight. miguel, thanks. nbc news has confirmed it was indeed ricin that was in those letters mailed to some officials in washington. it's been confirmed due to a second round of tests. today, 45-year-old paul kevin curtis was in a mississippi courtroom charged with making threats against president obama, mississippi senator roger wicker, and a local county judge. curtis happens to be an elvis

impersonator. senator wicker hired him a decade ago to work at an event. a lawyer for curtis said he was innocent. officials say none of this was related to the boston bombings this week. still ahead for us on this thursday night, cars swallowed whole during a morning commute. flooding so bad the ground is giving way in some places. a lot of folks are in for a wild one ahead. later the warning today from the f.a.a. the reason for major flight delays starting this weekend at a lot of the best known airports across this country.

take a look at the national radar and look at the front cutting north to south and moving to the east. it's a huge weather system stretching from the mexican border all the way into canada, dumping torrents of rain, snow, hail, spawning tornadoes along the way. it's left a lot of damage behind. the chicago area particularly hard-hit. nbc's john yang is in lisle, about 25 miles outside of

chicago. john, good evening. >> reporter: good evening, brian. the radar says there is more rain on the way. across the region rivers are still rising as forecasters are predicting record levels and massive flooding. chicago streets turned into rivers and lanes of major expressways shut down as heavy rain fell faster than storm sewers could carry it away. neighborhoods quickly flooded. in lisle, firefighters set out in boats to answer calls for help. >> we had to be prepared not only today but over the next several days for flooding in different parts of our state. >> reporter: on chicago's south side a car drove into a sinkhole which eventually swallowed two parked cars. north of the city in gurney, residents have prepared for flooding from the des plains river by sandbagging homes and businesses. >> we have been here about ten years. this is actually the worst it's

been. >> reporter: the river is expected to crest tomorrow morning at 11 1/2 feet, a record. officials are encouraging residents along the river to evacuate. >> it could be a week or two before flood levels significantly drop. >> reporter: parts of iowa and illinois have gotten more than seven inches of rain and totals approaching six inches are not uncommon. in south dakota the storm system brought snow and temperatures in the 20s. warmer weather in oklahoma spawned at least four tornadoes but no one was seriously injured. back in chicago, sump pumps are hot items. >> we've got the last one here. we got one from the front of the store. that's about it. everyone who came in behind us, i'm sure they didn't get one. >> reporter: cynthia gill and her family moved to lisle just last week. now their home is an island. their basement under water. >> my daughter floated on a mattress today to try to retrieve as much as she should. >> reporter: weather channel meteorologist mike seidel says the danger has not passed. >> although the rain and storms will end tonight in the midwest

all the water has to go somewhere. it is going to run into the rivers and many of those will go over their banks into flood stage as we head towards the weekend. >> reporter: of course thunderstorms means trouble in the air. at chicago o'hare airport, more than 600 flights cancelled because of weather. brian? >> john yang reporting on the weather for us tonight from lisle, illinois. john, thanks. we are back in a moment with word of a health scare tonight for a hollywood legend and his public request for help in figuring out what it is.

talk about a sentimental journey. this will warm your heart and we could use some of that right about now. of the 75 original doolittle raiders from world war ii only four men survive today. now three of them have gathered for what will be their last reunion. it included a flight in a beautifully restored b-25. during the original outlandish raids 71 years ago today 16

aircraft, all loaded with one-ton bombs took off from the deck of a carrier four months after pearl harbor with only enough fuel on board to drop bombs on tokyo and then land in china where they could only hope for safety. remarkable video out of the uk. it is rough but then again it was a rough day for landings at leeds bradford airport. in the midst of a 70 miles per hour gale, but land they did. crabbing into the wind on final approach. not even close to lining up with the center line of the runway, but all of them managed to straighten out in time. sadly in-flight drink service didn't include complimentary cocktails upon arrival. on the subject of air travel, sooner or later the so-called sequester in washington is going to affect all americans. like starting this sunday when

the air traffic controller furloughs start. officials warned today at airports like atlanta, chicago, o'hare, newark, jfk, laguardia, delays will start to be felt. upwards of 50 minutes on some flights at o'hare. some unsettling news about an american favorite. dick van dyke has been forced to cancel an appearance in new york because of an undiagnosed neurological disorder. he's asking for help with a diagnosis. on his twitter account, dick van dyke solicited assistance in figuring out what he's got. a throbbing condition in his head when he tries to lie down. it's led to lack of sleep and fatigue. it has eluded tests and scans so far. dick van dyke is 87 years old. and some good news to report from the world of public health. the nation's infant mortality rate fell by a full 12% in the years '05 to 2011, having been static for years. the biggest change for the better was in the south. but the u.s. still ranks an embarrassing 27th in infant mortality among the world's 30 leading developed nations. another problem for carnival cruise line.

this time on board the "ecstasy." it lost power at sea while sailing off the coast of florida with 2,000 passengers on board. the cruise line says there was no fire, no emergency. power was eventually restored. when we come back here tonight, the amazing moment from last night in boston.

finally here tonight in the wake of the marathon bombings, boston strong has emerged as the phrase and the iconography that the entire region has taken on. it was a tight town before this. it's even more so now. our own bay state native anne thompson has our report from there tonight. ♪ o say can you see >> reporter: the full-throated rendition of the national anthem at the bruins game came as no surprise. ♪ over the ramparts >> reporter: bostonians have always worn their patriotism on their sleeve or on their chest. peter rinig prints t-shirts for a living. what's the importance of the t-shirt?

>> to say who you are. >> reporter: this shirt bears a simple message in a city where today there are no degrees of separation. >> everybody in the city knows each other. i think that's what makes boston boston, you know? >> reporter: he knew crystal campbell, one of the three people killed in the attacks. some of the money from the t-shirts will go to her family who today met with president obama. >> your daughter crystal was always smiling. ♪ >> reporter: at the interfaith service, mayor thomas menino, recovering from a broken leg, personified his city as he stood to speak -- wounded but determined. >> because this is boston. a city with courage, compassion, strength that knows no bounds. >> reporter: you could see its strength in the arms that reached out to rescue and comfort. one man literally giving the shirt off his back during those first chaotic moments. in the hands that gave out food and wrote checks. when those arms grew weary --

♪ o, say does that star spangled ♪ >> reporter: voices were raised in the city where the american revolution began. ♪ the land of the free >> reporter: the hub of america today is its heart. anne thompson, nbc news, boston. ♪ and the home of the brave >> on that strong note, that is our broadcast on a thursday night. thank you for being here with us. i'm brian williams. we, of course, hope to see you right back here tomorrow evening. good evening everyone, i'm in for raj mathai. >> we'll have more on the first lady's visit with the local victim on the attack.

and we begin with the investigation, free time off for the selective employees in the district attorney's office. our investigative unit first broke the story this month. santa clara district attorney jeff rosen giving time off to the staff, to make up for the 5% bonus cut. >> we have just learned county council has issued its opinion on the legality of the district attorney giving free time off. it is a confidential document delivered to the board of supervisors. the sources close to the county's investigation says it does not look good for the da. one problem is how it could open up for others in a big way. others call it the me-too clause. >> reporter: letter after letter. >> there is a lot of animosity towards mr. rosen right now. >> reporter: different unions, same concerns. >> we had an understanding, a trust, an agreement.

a contract. and we did not expec to be sitting here today. >> reporter: it comes after our investigation exposes the district attorney, jeff rosen, suggest that time sheets be alter altered, allowing employees to bank vacation and sick time which they can later use. he made up for a 5% bonus cut in the middle of the budget crisis. >> so yes, i brought in administrative leave to try to compensate them in some way for that. >> reporter: that answer would be a costly one for the county. >> it is a public gift that the public didn't know they were giving away. >> reporter: the santa clara county peace officer's association had to make drastic cuts to help the county. >> for us it is a huge slap in the case. >> reporter: unions are now pointing to the me-too clause in their county contracts. it means if one county didn't take the cuts promised, others don't have to either. >> all we're asking for myself and the association is to be treated fairly. that means that the county has

to come down a little bit on jeff rosen and what he is doing, is to get things corrected and that it what should happen. >> but if the county is not going to do that because he is an elected official then they have no other means other than to make everybody whole. which means fair share for everybody else. >> reporter: sergeant dennis moser is the president of the association. >> because you're an elected official doesn't put you above the law. >> reporter: other unions are also demanding answers. the registered nurse's union says they intentionally violated the agreements. the building and construction trade writes it is wrong regarding the association. others talk about how it could impact the budget. >> it is very important how we get the contracts buttoned up and that nobody did something like that. >> reporter: rosen still stands by his decision, calling the 5% bonus cut unfair. >> that is not fair to p