on the broadcast tonight. an aspirin a day that could help prevent and treat cancer. the new research that's being called a game changer. the early reports of damage after a big hit there. final moments. there's news tonight about the last phone call in that florida shooting that has sparked national outrage and n a federal investigation. and the enduring mystery. what happened to amelia earhart. tonight one of the world's most powerful women joins in the search for one of the world's most famous women. "nightly news" begins now. captions paid for by nbc-universal television

good evening, we are going to begin here tonight with a story from the world of medicine that could end up affecting every american. this is a story about cancer, it's treatment and prevention, and this time it's a story about aspirin. it's without question the cheapest medication in the american household. its role in preventing heart disease and strokes is well documented. we call it the wonder drug. this is about something else. it's new evidence tonight having to do with the role aspirin plays in preventing certain kinds of cancers. we start off tonight with dr. nancy snyderman. >> reporter: like so many americans, dana started taking an aspirin a day ten years ago to prevent heart disease. after being diagnosed and treated for colon cancer, his doctor told him to stay on it. >> aspirin therapy was something they thought of as a healthy

recurrence of cancer. >> reporter: the medical journal says aspirin may have a new role in cancer prevention and treatment. people who take aspirin had a 15% lower risk of dying from cancer. a 38% less chance of developing colorectal cancer. and aspirin may reduce the risk of cancers of the esophagus, stomach, breast and lung. it may provide benefits after diagnosis. aspirin mayri may have a 36% chance having cancer spread. >> aspirin may have an additional benefit in terms preventing cancer. we also know that it's not a panacea. >> reporter: doctors caution that aspirin still carries risks. it can cause stomach upset and bleeding. these new findings suggest the risks of cancer prevention outweighs those risks. >> my patients will often ask me

is there something i can do to make my treatment better? the answer has often times been no. then something like this comes along, and we forget about aspirin. it can be helpful. >> doctors insist you should watch what you eat, exercise and avoid smoking. this little pill, an aspirin that just costs pennies a day, this is one of those things you may add to that list. >> because it's ubiquitous and cheap, so many people are just going to want to run to this. who should be cautious, really? >> no doctor's going to say, everybody should be on it, but increasingly, doctors are encouraging folks. i think the subset of people who should be alarmed or hedge a little bit are people with any bleeding disorders, people who have had problems in the past, and certainly you have to have your conversation with your doctor. the real advice today, especially remember, take the cheap stuff. the white crumbly aspirin you can see falling apart in the bottom, that's what gets in your

system quickly. this humble little medicine is increasingly sophisticated and could be a lifesaver. >> thank you, nancy. as we mentions at the top of the broadcast, a large and long lasting earthquake struck the southern part of mexico today. this one measured a 7.4. it was centered about 370 miles south acapulco. a lot of people were scared, despite some heavy damage. there are no reports of early deaths as of yet. malia obama is in mexico on a school-sponsored service project in an area where the quake was felt, but the white house says she is safe and was never in danger. in texas, a tornado swept through devine outside san antonio last night. damaging homes but causing no

injuries. one of three twisters confirmed today by the national weather service. the same storm system brought hail, high winds, also flooding to parts of texas, oklahoma, kansas and arkansas got a pretty bad flood watch and warnings are in effect until thursday. 85 degrees in chicago by the way. now to the army staff sergeant accused of murdering 16 afghan civilians earlier this month, robert bales' lawyer spoke today after a long session with his new client. our report tonight from nbc's john yang. >> in 11 hours of conversation, staff sergeant robert bales told his defense attorney his memory the night of the shootings is spotty. >> if you woke up and didn't realize what you had done last night, and people were telling you had done some really awful things and you had no memory of that. that kind of gives you an idea of what i'm talking about. >> john henry brown has seen

this kind of thing before. in cases involving head injuries, like the one bales suffered in iraq. he questioned the strength of the military's case against his client. >> there's no forensic evidence, no medical examiner's evidence. there's no evidence about how many alleged victims or where those remains are. so it's fascinating. >> reporter: as the military's criminal investigation continues. the u.s. commander in afghanistan announced an investigation into bales' chain of command. >> it will look at the entire command and control process, how he was assigned, why he was assigned. >> reporter: outside seattle, movers emptied the house where bales lived with his wife and two small children as details emerged about his background. when with he was a stockbroker, he and colleagues engaged in fraud, breach of fiduciary trading. he failed to pay a $1.2 million

fine and was suspended from the industry but he had already enlisted in the army. brown didn't ask bales about it. it's too early to tell how he'll defend bales, but made clear his client won't be the only one on trial. >> i think the war is on trial. i think the war should be on trial. and i'm hoping that the war will be on trial. brown says the army is trying to arrange a visit by bales' wife. they've only been able to speak once by phone since he was arrested, that's when he was being held in kuwait. they expect charges to be filed sometime this week. his attorney says he expects them to include murder, which carries the death penalty. >> john yang ft. leavenworth, kansas tonight. it's another summer like day in march in illinois today. it's another gop primary evening in our never ending political season. nbc's peter alexander is withed romney campaign on the trail in

illinois. good evening. >> reporter: a state with a lot of moderate republicans, mitt romney is expected to win. to give you a sense of the dilemma facing republicans here and across the country, consider what bob michael, a retired veteran house leader from peoria told me just this week. he's supporting romney, but he worries heels not a very exciting candidate who can rally republicans behind him. he is missing that magical spark. romney is trying to cast himself as the presumptive nominee, focusing his attacks almost exclusively on the president. yesterday at a speech at the university of chicago, where president obama taught, he attacked the president 12 times by name in less than 18 minutes. brian? >> peter alexander on the campaign trail tonight. thanks. one issue that's been percolating through this presidential primary season, a push to limit women's access to

contraceptives and abortion and it has some wondering how it might affect the general election. our report from andrea mitchell. >> reporter: across the country, protests lying this one in texas, against new state laws restricting access to contraception and other women's health care. >> maybe they don't want us to have freedom, but we're fighting back. >> reporter: a fight college students took to mitt romney monday night. >> you're for freedom and all this stuff. >> absolutely. >> you know what would make me happy, free birth control. >> if you're looking for free stuff, if you're looking for free stuff you don't have to pay for, vote for the other guys, that's what he's all about okay? >> reporter: contraception is not okay, calling a license to do things in a sexual realm that is counter to how things are supposed to be. in 39 states, legislators with similar views are rolling back access to contraception or

abortion or considering proposals. >> i think what we're seeing across the country andrea is so many legislatures that are doing everything they can to shame women, and to make it more difficult for them to get health care. >> reporter: arizona's legislature would force women to prove to employers that they are using birth control for medical reasons not contraception. pennsylvania would require sonograms before abortions. a proposal the state's governor defended because it wouldn't be invasive. >> i don't know how you make anybody watch, okay? you just have to close your eyes. as long as it's exterior, not interior. >> comments like his only added to the growing outrage. >> i think the election is going to be about choice, and it's going to be pretty clear for women who's on their side regarding their health care issues. >> reporter: santorum's wife karen is trying to reassure women her husband won't impose his views on them.

>> women have nothing to fear when it comes to contraception, he will do nothing on that issue. >> reporter: andrea mitchell, nbc news, washington. still ahead here tonight, the final phone call before the shooting death of that teenager in florida, and the young woman who was on the phone with him as the situation took a dangerous and terrible turn. she disappeared 75 years ago, trying to fly around the world. why hillary clinton has joined in the hunt for amelia earhart. look! the phillips' lady!

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in florida tonight, demands for the arrest of a neighborhood watch volunteer who shot and killed an unarmed teenager last month, they're demands that are growing in the wake of revelations from a victim's girlfriend that she was on the phone with him as the incident happened. and the involvement of the justice department, the other new development if this case. nbc's ron allen with us tonight from sanford, florida.

ron, good evening. >> reporter: good evening, brian. there are hundreds of people trying to jam into this small little church here, to demand an arrest in the case of trayvon marlton. hundreds of people are also down here on the streets trying to make their way here. in washington today, the justice department said it would investigate the case. here in florida, the states attorney said he would lay the case out before a grand jury and let them decide. the martin family layed out more proof that he was an innocent victim. they played recordings of a phone conversation between he and his girlfriend at the moment the confrontation with with george zimmerman began to unfold. >> she hears another voice say, what are you doing around here? >> then she heard what sounded like an altercation. george zimmerman shot and killed trayvon martin in self-defense. a shooting with no racial overtones or hate crimes. but when zimmerman was calling

police the night trayvon was killed he used a racial epithet. >> what entrance is he heading toward? >> the back entrance. [ bleep ]. >> reporter: all of this is igniting more demands for an arrest. the online petition has more than half a million signatures. for many here, the martin case is not an isolated incident. just last year, when a police officer's sun assaulted a black man outside a bar, it took a month before charges were filed. in 2005, murder charges against two white security guards were dismissed after a black teen was shot dead. >> this is where it happened? >> yes, just about right here. >> reporter: if this quiet and comfortable community where there had been a rash of communities, neighbors are outraged by whatny heard. >> are you following him? >> yeah. >> okay, we don't need you to do that. >> he's not charles bronson, and

this wasn't "death wish." this isn't a movie, it's an actual thing that's happened out here. i really hope the fbi can get to the bottom of it. ♪ >> reporter: black parents have been warning their young sons to be careful for years. she hopes the martin family gets some measure of justice. >> we don't feel like justice has been done. we want an arrest. we want all the questions answered as much as possible. >> reporter: this is just one of several protests and town halls planned for this week. hearing those 911 calls, hearing the police tell zimmerman to back off, hearing martin's cries for help have turned up the intensity here. and again, zimmerman was nowhere to be found. >> ron allen, thanks. a program note, trayvon martin's parents will be here in our new york studios tomorrow morning on "today" for an exclusive interview. the queen's speech, marking

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it would be a real treat to hear this monster fire up. [ jaronda ] i think a lot of people, when they look at a jet engine, they see a big hunk of metal. but when i look at it, i see seth, mark, tom, and people like that who work on engines every day. [ tom ] i would love to see this thing fly. [ kareem ] it's a dream, honestly. there it is. oh, wow. that's so cool! yeah, that was awesome! [ cheering ] [ tom ] i wanna see that again. ♪ [ tom ] i wanna see that again. it's oysternomics 101. you start with a u.s. senator named ben. by helping restore thousands of acres of oyster beds, he kept hundreds of oystermen on the job... which keeps wholesalers in business... and that means more delivery companies... making deliveries to more restaurants... which hire more workers. and that means more oystermen. it's like he's out here with us. he's my friend, ben.

i hope he's your friend, too. i'm ben cardin, and i approved this message. big news in the fast food community tonight. there's been a change near the top. wendy's has bumped burger king for the number two spot. edging out burger king for the first time since wendy's was founded in 1969. mcdonald's trumps both and by a big margin. the queen celebrated her diamond jubilee. it's been 60 years since her coronation to the thrown following the death her father. she paid tribute to virtues of resilience resiliency. >> in an era where the regular worthy rhythm of life is less eye catching than doing something extraordinary, i'm

reassured that i'm nearly the second woman to celebrate a diamond jubilee. >> she had kind words for her husband prince phillip. she called him a constant strength and guide. the first lady revealed a little more about those secret shopping outings she's sometimes been able to take just to get out of the white house bubble. last night on the late show, she told david letterman about a woman she encountered recently at target. >> no one knew that was me. because a woman actually walked up to me, right? i was in the detergent aisle, and she said. i kid you not, excuse me, i have to ask you something. and "thought, cover's blown. she said, can you reach on that shelf and hand me the detergent? i kid you not. >> the woman not knowing who she had just spoken to said to the very tall first lady, you didn't have to make it look so easy.

it's going to be possible to fly from clinton to reagan and with continuing service to kennedy and bush. the little rock commission has unanimously voted to rename the airport after bill and hillary clinton. just ahead tonight after the break, what happened to amelia earhart. a new clue. oh. let's go. from the crack, off the backboard. [ laughs ] dad! [ laughs ] whoo! oh! you're up! oh! oh! so close! now where were we? ok, this one's good for two. score! [ male announcer ] share what you love with who you love. kellogg's frosted flakes. they're gr-r-eat! is non-stop to seattle? just carry preparation h totables. discreet, little tubes packed with big relief.

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ask your doctor about cialis for daily use and a 30-tablet free trial. i'm here to unleash my inner cowboy. instead i got heartburn. [ horse neighs ] hold up partner. prilosec isn't for fast relief. try alka-seltzer. it kills heartburn fast. yeehaw! i get my cancer medications through the mail. now washington, they're looking at shutting down post offices coast to coast. closing plants is not the answer. they want to cut 100,000 jobs. it's gonna cost us more, and the service is gonna be less. we could lose clientele because of increased mailing times. the ripple effect is going to be devastating. congress created the problem. and if our legislators get on the ball, they can make the right decisions.

we wanted to show you this, heroes in the balcony. not every day you can look up from the floor and see 31 recipients of the medal of honor ringing the bell, including jack jacobs in the front row, left of center. we salute them all. and finally here tonight. she was a global celebrity and her disappearance has been one of the great enduring mysteries of the last 75 years. amelia earhart was fearless, a natural flyer and way ahead of her time. on a july day in 1937 she disappeared while on approach to a remote pacific island. the search started an hour later and hasn't stopped since.

it's about to get a boost. our report tonight from chris jansing. >> amelia earhart, america's heroine in the days when flying meant adventure. >> reporter: seen here with her husband, before an attempt at an unprecedented around the world flight. >> how about taking me along? >> well, of course i think a great deal of you, but 180 pounds of gasoline on the flight may be a little more valuable. >> the world was captivated. >> miss earhart made a great hit over there. >> on the final leg of the journey, her plane disappeared. >> we're intrigued and entranced by the story of this attractive modern woman who sets off on the flight of her dreams and never comes back in. >> now, new forensic imaging analysis of this grainy photo taken just three months after

earhart disappeared may reveal clues to her disappearance. in july, the international group for historic aircraft recovery will launch a deep water search for the plane, earhart's remains and the cliffhanger so tantalizing it brought out one of the most famous women of our day. >> we too could use some of amelia's spirit. >> the plane simply ran out of gas and crashed some say. expedition leaders believe earhart may have survived that crash, a castaway on an island between hawaii and australia. finding the airplane could finally mean a conclusive answer. >> she carried the aspirations of our entire country with her. >> and now a team of modern explorers will take with them the curiosity of generations. chris jansing, nbc news, new york. and that's our tuesday night

broadcast. thank you for being here with us. i'm brian williams. we, of course, hope to see you right back here tomorrow evening, good night. -- captions by vitac -- www.vitac.com