this is "nightline." >> breaking news. u.s. forces on the attack. tonight, launching military air strikes against i.s.i.s. in syria. the mission, to degrade and destroy the brutal islamic terror group. fighter jets, bombers and tomahawk missiles bearing down on i.s.i.s. strongholds. as a flood of refugees flees the region. we're there with the latest. and vanished. the desperate search for missing uva student hannah graham continues. now, the man police say was with her last is gone, too. >> we want to talk to him. >> did they let him slip away? what we're learning tonight, as her parents beg for clues to find their baby girl.

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good evening. thanks for joining us. breaking news as we come on the air tonight. american forces on the attack. the first wave of u.s. air strikes hitting i.s.i.s. targets in syria, opening a new front in the battle against the islamic terror group. for the very latest, we turn to abc's chief global affairs correspondent, martha raddatz. >> reporter: juju, this is the biggest wave of air strikes we have seen in a single day since the u.s. began attacking

i.s.i.s. in early august. and we did not do it alone. five arab nations joining in the strikes, which pounded some 20 targets in the area of raqqa. that's an i.s.i.s. stronghold, and believed to be the area where those american and the british hostage were executed. the air strikes carried out by a combination of u.s. stealth bombers and stealth fighters and tomahawk missiles launched from the sea. in fact, the f-22 raptor, an expensive stealth fighter used for the first time in combat. the targets, i.s.i.s. safe havens. command and control and logistic centers. twitter lit up with reports of huge explosions around raqqa. the other arab nations taking part, all largely sunni, including jordan, saudi arabia, bahrain, qatar, and the united arab emirates. the kind of coalition the u.s. has been trying to build to go after i.s.i.s.

but a big step here tonight as the u.s. expands the fight against i.s.i.s. into syria, where the president was loathe to go for so long. but he gave the go ahead for these strikes. and throughout this evening, he has been briefed on the progress. tomorrow, he heads to new york and the u.n. we do expect to hear from him then. these air strikes will be ongoing. the chairman of the joint chiefs of staff says the fight against i.s.i.s. in syria will be persistent and sustainable, which means this will likely continue for months on end. juju? >> martha, thanks, as always. and joining me now, abc news chief investigative correspondent, brian ross, who has been tracking the growing terror threat. posed by these violent extremists. brian, now that u.s. air strikes are under way, what might this mean for i.s.i.s.? >> this is a ruthless group, whose members seem to enjoy their medieval barbarism. the limited u.s. air strikes led to a round of beheadings. as president obama promised a heavier round of attacks,

i.s.i.s. escalated its threats to america, in anticipation of what did happen tonight. as i.s.i.s. turned up the tempo on its propaganda machine today, with new videos of its military-like formations, and dire threats to american civilians, u.s. officials revealed details of a promised crackdown on westerners who want to join i.s.i.s. or already have, like these britons who appeared in a new video today. >> we are working closely with our international partners to mitigate this threat. keep eyes on these individuals and monitor their movements. >> reporter: u.s. officials said today, efforts to shut down the jihad pipeline to i.s.i.s., will focus on boston, minneapolis, and los angeles. cities that have already sent a number of young recruits to i.s.i.s. basic training. the kind of young men and women, seen in this latest video, parading in uniform, with brand-new ak-47s. the urgency of the coming white house push against i.s.i.s., was underscored today by one of the

terror group's weekend propaganda messages. its chief spokesperson earned supporters around the world. if you can kill a disbelieving american or european, especially the spiteful and filthy french, or an australian or a canadian, then rely upon allah and kill him in any manner or way, however it may be." and today i.s.i.s. followers in nigeria posted this video of a 55-year-old french citizen who they said they kidnapped and would behead in 24 hours, unless the french stopped its bombing of i.s.i.s. positions in iraq. as for i.s.i.s. itself, it is currently believed to be holding some 15 western hoarsages, including two young americans, all of whom have been threatened with execution. juju? >> brian, is it possible that the air strikes cover for a potential rescue mission? >> that's possible. we don't know that, won't know that for a while. but what we do know is u.s. authorities said if there was any chance, they would try to

mount a second attempt. we know that in flying over the area with drones and satellites in place, looking not only nor command and control centers but any indication whatsoever of where the hostages might be held. >> this is the first step in a major campaign. thanks for that update. we turn to alex marquardt, who spent the day talking with refugees, fleeing the threat of i.s.i.s. he's just across the border from syria and joins us from turkey, where there was already a mass exodus under way even before tonight's air strikes. alex? >> reporter: good evening, juju. the past several days have seen i.s.i.s. pushing into northern syria, surrounding and taking over predominantly kurdish towns along the border with turkey. that has sent an unprecedented number of refugees streaming across the border into turkey. the u.n. says more than 130,000 over the past four days. that is the biggest single exodus of refugees since this war in syria began over three and a half years ago.

we met many of the refugees who told us, if they stayed behind, they would have been executed by i.s.i.s. they came with what little they could carry. and angrily told us that the u.s. is doing nothing to stop the i.s.i.s. advance. that is before these air strikes started. many of the refugees in turkey will be happy to see the air strikes carried out by the u.s. and the other countries. at the same time, it could set off a new wave of refugees, fleeing for safety from those areas where i.s.i.s. is operating. the u.n. and turkey already preparing for many more refugees to cross the border. juju? >> alex, thanks. our thanks to alex marquardt, reporting from the region. stay tuned to abc news for all the latest on these breaking developments. up next for us, the anguished parents of a missing college student speak out as more than 1,000 volunteers join their urgent search. now police are looking for the man last seen with her. what evidence do they have? and what does he know about her disappearance?

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tonight, a desperate search intensifies as the mystery deepens in the disappearance of college student hannah graham. the 18-year-old university of virginia coed vanished ten days ago without a trace. now authorities zeroing in on the man last seen with her. but what does he know about her final moments in public? and why can't police find him tonight either? here's steve osunsami. >> did you see hannah? did anybody see hannah? did you see hannah? did you see hannah? who saw hannah? >> reporter: by the time america got to know hannah graham she was already missing. >> i can't imagine what this family's going through. i was talking to her mom the

other day and it's just really -- sorry. >> reporter: the 18-year-old second-year student at the university of virginia disappeared ten days ago. >> this is every parent's worst nightmare. >> reporter: and now the one man who might know the most -- >> i believe if jesse matthew was the last person she was seen with before she vanished off the face of the earth. >> reporter: has gone missing too. >> we want to talk about his interactions with the sweet young girl we can't find. because he was with her. >> reporter: tonight police are poring over evidence they took from his apartment. >> shirts taken from the house? >> clothing, articles of clothing, i specifically don't know what they were. my conversation with the detective was very brief. >> reporter: they issued an arrest warrant after an incident with police but they haven't named him a suspect in the mysterious disappearance. >> it's kind of hit home that this is something that can really happen. before it was more stories and warnings. now it's a real person who's gone. >> reporter: it all began ten

days ago on a friday night after a tough week of classes. there were parties on every corner and graham like so many students was ready to have a good time. this is the last place her friends remember seeing her. at a party at this apartment complex called camden plaza around 12:15. at around 12:45, video outside of mcgrady's irish public shows her crossing a small overpass alone. just before 1:00 a.m. cameras show her running but doesn't appear anyone's following her. a little while later another camera sees her at this downtown mall. now you can see she was being followed. police say the man following her was in fact a good samaritan who they don't believe was a suspect. concerned she was intoxicated, he says he backed away once he saw her looking very comfortable with someone who looked like a friend. that friend, police say, was 32-year-old jesse leroy matthew, a nurse's aide working at the university of virginia hospital. >> you can clearly see this black male with dreadlocks cross

to the other side of the mall, then he travels eastbound behind her. >> reporter: finally, in this video, police say you can see him walking beside her out of frame. the very last image that exists of hannah graham. >> it's been a week and we can't find her. but somebody knows where she is. >> reporter: we know they went to this restaurant and bar on fifth street called tempo. this is where the timeline grows cold. police believe they might have gotten into this orange car. >> his car was seen leaving the area on video. and we have every reason to believe that miss graham was in that vehicle. >> reporter: over 1,200 volunteers began combing the area looking for evidence that might bring her home. it didn't take long for police to meet matthew, seen in this facebook photo. first they searched his home and then seized his car on friday. but they didn't arrest him. he walked into police headquarters saturday. >> he got inside, he asked for a lawyer, we found him one. and i don't know any more about his interaction with hannah graham than i did when he walked in. detectives don't know any more about the interaction he had

with that young girl. any more than the moment he walked in. so i hope and pray that we might have opportunity to talk to jesse matthew again. >> reporter: that's when police say he dangerously sped away in his car and the police who were tailing him decided to let him go. that may have been on purpose. >> he may take you to potentially a body, evidence, a weapon. whatever it might be. a secluded location. they panic, destroy evidence or leading you to evidence, so let him go and see if he leads them to more evidence. >> reporter: and this afternoon, they were back at his apartment. taking out bags to be sent to a lab. >> i think what they've done is gone back to see a number of things. are they armed now with more information? about potentially what happened or could have happened? are there areas of his living quarters that didn't get adequately searched, items that belong to her?

it's sort of all the above because the real key in this case, obviously, is how can they link her disappearance to jessie? >> reporter: this isn't the first disappearance in virginia. the list of missing is long. so many cases. families crying out just like the grahams. this year alone, 116 missing in virginia. all under 20 years old. >> i think the whole idea of holding somebody hostage for weeks, months or years is probably not a realistic hope. it's happened. we've talked about these cases in the recent past. but it's not a common thing. when they disappear like this, and we don't hear anything for days, weeks or months, the presumption is something has happened to them. >> reporter: virginia police underline they have issued a warrant for jesse matthews' arrest for reckless driving but not for the disappearance. they hope that brings him in. they warn the public this is far from over. >> i don't want anyone out there in this community still looking for hannah graham to get tunnel

vision just because we have a name. >> reporter: friends and family are still holding on to hope that this student, this daughter, will return. her parents speaking out for the first time this weekend. >> she's enormously precious to us. somebody knows what happened to hannah. all we want to do now is to bring hannah home safely. and i appeal to anybody who knows anything, please, please help us. >> reporter: for "nightline," i'm steve osunsami in charlottesville, virginia. >> our thanks to steve for that report. stay with abc for the developing details in that story. next up for us, move over, dogs. man just might have found a new best friend. we're revealing the secret life of cats and the hidden messages behind those meows. what they're really trying to say may surprise you. we ed her fever. you raise her spirits. we tackled your shoulder pain.

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okay. think about this. do cats have superpowers? can they save not only their own nine lives but yours, as well? my cat-loving co-anchor, dan harris, revealed surprising truths guaranteed to make sure you never think of your feline friends the same way again. >> want to say hello to the camera? >> reporter: as a dude who loves cats, i spend a lot of time defending myself against haters. but this new documentary from nat geo, called "the secret life of cats," provides me with useful ammunition. think cats are hopelessly wussified? this cat may have saved her owner's life. she left the stove on. the place would have exploded when the heating came on at 4:00 a.m. but basil smelled trouble and

woke his owner up. >> he went like that. one little claw. and i knew there was something wrong. he is my hero. aren't you, hey? >> reporter: think cats don't care about anybody other than themselves? this blind and partially deaf dog lived most of his life in bed. until he found a seeing-eye cat. >> he seemed to know there was a need there somehow. i don't think i've seen some get along as well as these two. they rely upon each other. in that same way. >> here we are, with a compliant gus harris. his ears are back. he's looking displeased. >> reporter: nat geo sent this veterinarian to my apartment to meet my cat. >> one thing that's surprising. once in a while, one of the cats will rub against me. i always thought that was a sign of affection. but it's actually not. >> it's saying, you're mine. i'm marking you. >> reporter: as the film explains, cats need to mark everything and everyone with

their scent so their world stays familiar to them. >> we're going into the closet. >> reporter: while two of the three of my cats spent the interview hiding in the closet. why do they like being in little spaces? >> they like being secure. they like to know what's around them. >> reporter: the documentary is filled with fascinating facts about cats i never knew, even though i lived with these creatures my entire life. why do cats do that thing when they give you an unsolicited massage from their paws? it stems from when they emerge from the womb deaf and blind, and they have to knead their mom's belly to find her milk. when they do that to you, they're re-creating the comforts of kittenhood. and what are the whiskers for? they are sensitive navigation tools. even blind cats can find their way around, using whiskers the way blind people use a stick. and we all know cats pretty much always land on their feet. but nat geo used high-speed

cameras to see how they do it. >> you'll see a cat in less than ten seconds. all of a sudden you realize, oh, here's down. and they get the front end oriented correctly. then the back end gets into position. they extend their little legs, get their claws out. when they hit the ground, they're not going to slip. arch their backs so they have that spring in their suspension system. it's like, oh, okay, fine. survived that one. >> reporter: this cat, sugar, survived a fall from the 19th particular of an apartment in boston. >> they looked all over. no broken bones at all, just light bruising to her lungs, that's it. no chipped teeth, nothing. no scratches. >> reporter: this film with all of its secrets and moving stories, may play its little part in eroding the p.r. problem facing cats. >> many times people think they're aloof. and they're really not. they're just a different species. a whole different animal. they are loving. once you get to know them. they're not going to love like a

dog. but they have great senses. when you bring them into a house, it's always for life. >> reporter: for "nightline," this is dan harris, in my apartment. >> i didn't think he could be even more obsessed. "the secret life of cats" airs thursday, october 2nd, on nat geo wild. "world news now" is coming up soon with overnight breaking developments on u.s. air strikes against i.s.i.s. in syria. and tune into "good morning america" tomorrow for a full report, as president obama travels to new york for the u.n. general assembly. thanks for watching abc news. good night, america. have a good one. ood night.

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