this is "nightline." tonight, the american sniper trial. as moviegoers flock to theaters for the true story of military legend chris kyle, the real-life final act playing out in court today. kyle's widow on the stand and in tears testifying against the troubled veteran who killed her husband. what made him turn on somebody who was just trying to help? whitney and bobbi. on the anniversary of whitney houston's death, officials now confirm that bobbi kristina's case is a criminal investigation. tonight as bobbi kristina clings to life, family friend kevin costner speaks out. and the theory of eddie. >> i am an addict. for acting.

>> he went from peak physical fitness in "jupiter ascending" to heartbreaking decline in "the theory of everything" as stephen hawking. now actor eddie redmayne reveals how he transforms into an icon. but first, the "nightline 5." >> if you struggle with back pain you have the power to turn it off with this. >> smart relief from icy hot. turn on relaxing pulses to quickly block even chronic back pain. wireless, reusable, and easy to use. >> turn on relief and turn off pain. i'm making extra cash as a laboratory test subject. >> i'm comfortable with that. any side effects? >> when your mattress is this comfortable you'll be comfortable with anything. the i-comfort sleep sister territory by serta. featuring memory foam with dual action gel technology. experience i-comfort. >> number one in just 60 seconds. huh, fiftepercent or more on e you fifteen percent or more on car insurance. everybody knows that. well, did you know words really can hurt you? what...?

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good evening. his story has captivated moviegoers all over america. chris kyle, the so-called american sniper, a military legend. today, in court, the man who shot him to death went on trial for murder. the defendant is a troubled veteran whom kyle was simply trying to help. today we saw emotional testimony from kyle's widow and a revealing text message kyle sent shortly before he died. here's my "nightline" coanchor byron pitt. >> hold on, i got a woman and a kid 200 yards out -- >> reporter: it's the blockbuster movie millions have flocked to theaters to see. bradley cooper as the real-life american sniper chris kyle. but not seen on screen how kyle was gunned down, allegedly by marine veteran eddie ray ralph. >> 911, what's your emergency? >> he said that he killed two guys. >> reporter: ralph, these pictures from his time in iraq, is the man accused of gunning

down kyle and his friend chad littlefield at a shooting range in february 2013. kyle leaving behind his wife tea. >> i am now and always will be the wife of a man who is a warrior both on and off the battlefield. >> reporter: today, the much-anticipated trial in texas beginning. >> and they found chris kyle shot five times in the back and side. one time in the back of the head. >> reporter: the defense claiming ralph is not guilty by reason of insanity, arguing ptsd from his time in the military made him turn the gun on two men trying to help him. >> when he took their lives, he was in the grip of a psychosis. >> reporter: first to take the stand, chris kyle's widow tea. she isn't buying ralph's defense. today in court she said as much with tears as she did with words. while the judge has banned audio recordings of witnesses, my colleague ryan owens is in the courtroom.

>> one of the prosecutor's first questions, who were you married to? tea could barely whisper the words "chris kyle." >> reporter: a wife's plea to the jury made up mostly of women, ten women, two men. >> i'd be far more concerned about the fact that it's ten texans than ten women. texas is not where you want to be presenting an insanity defense if you're the defendant. >> is it enough for the defense to say there's evidence of this guy was mentally ill, for him to therefore not be held responsible for the deaths? >> not enough to just say he was mentally ill. you have to be able to demonstrate the mental illness was so severe that he didn't understand what he was doing is wrong. >> reporter: the blockbuster movie hangs heavy over this case. the highest-grossing war film of all-time. how would you describe chris kyle? >> awesome. because he's so imposing. he's clearly an individual that you would never, ever want to mess with. >> reporter: it all made the search for an unbiased jury a difficult task. potential jurors had to fill out a four-page questionnaire,

gauging the details of the chris kyle story. >> the jury in this case is not being sequestered. why? >> sequestering a jury is a big deal. they're almost never sequestered. it's an enormous burden. >> reporter: kyle's legacy was larger than life. 7,000 people in attendance at cowboys stadium for his funeral. >> chris always said the body will do whatever the mind tells it to. i'm counting on that now. >> reporter: just a little over a week ago the governor declared a chris kyle day in texas. >> chris kyle day. >> reporter: notoriety aside the question for this jury is not if ralph pulled the trigger, but rather, what drove him to do it. >> -- when he shot these men, was it intentional and knowing? causing his death. >> reporter: the eddie ralph they're seeing today in court is very different from his mug shot two years ago. in a stark difference from these pictures, trying to hit home the insanity defense in opening arguments the defense presented text messages between chris kyle

and chad littlefield as they rode to the gun range with ralph in the back seat. >> i think it's very helpful to the defense that chris kyle himself is saying, this dude is straight-up nuts. because that's exactly what the defense is saying. >> reporter: prosecutors hope to paint an even more extreme picture. ralph with a history of violence and drug abuse. >> he admits that he murdered these two men that he'd used drugs and alcohol that morning, and that he knew what he was cog doing was wrong. >> reporter: prosecutors alleged he showed up at a family dinner and made threats to kill family members and himself, leaving shirtless, crying, and intoxicated. what's more, while in jail for a drunk driving conviction in 2012, prosecutors say he told officers, i'm a marine, i have ptsd. author laura beil of "the enemy within: the inside story of eddie ray ralph, the man accused

of killing the legendary american sniper chris kyle," spent time with ralph's mother. >> he was raised just like a texas boy would be raised. he had been kind of rebellious as a teenager. he was really intent on joining the marines. >> reporter: his mother telling beil he was very disturbed by his time overseas and in haiti during the earthquake of 2010. >> he wouldn't talk a lot about it. but they did notice something was different about him. by the time he came home. >> reporter: ralph's mother had reportedly sought help for her son. she approached chris kyle, who she knew was well known for his work helping veterans. >> he said, i'm going to do everything i can to try to help your son. >> reporter: brandon webb, also battled ptsd. insisting it's a treatable diagnosis, not a defense for murder. >> i don't believe he suffered from ptsd. i believe he was mentally ill. and i think that's a big difference. and had chris known that this was a person that was suffering from mental illness, not a veteran suffering from

post-traumatic stress, i don't think chris would have ever found himself on the shooting range with this guy. >> reporter: back in the courtroom today, the prosecution argues the same sentiment. >> mental illnesses don't deprive people of the ability to be considered to know right from wrong. still obey the law. and at the very least not murder people. >> reporter: the defense argues the system may have failed him. >> eddie ralph was suffering from a severe mental disease that he did not know his conduct was wrong. >> reporter: however eddie ray ralph's trial ends the debate over ptsd, mental health, the high price our veterans pay, all will linger a long time, as will the legacy of chris kyle, the american sniper who risked his life to serve his country. a story more compelling than any hollywood could produce. i'm byron pitts for "nightline" in new york. up next on "nightline," what

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three years ago today the singer whitney houston was found dead in a hotel bathtub. tonight her daughter bobbi kristina is in a coma after she too was discovered in her bathtub. but there is a key difference between these two cases. today, police revealed they are conducting a criminal investigation into what happened to bobbi kristina. and my "nightline" coanchor juju chang has more on that. ♪ come on clap your hands ♪ >> reporter: theirs was a mother-daughter bond that flourished in the limelight. but three years ago tonight, that relationship severed when whitney houston, one of the most celebrated voices of her generation, drowned in a bathtub in a beverly hills hotel with a cocktail of drugs in her system. tonight family members praying for houston's daughter bobbi kristina brown, who was found in

an eerily similar scene in her home in georgia. tabloids have been reporting bobbi kristina would be removed from life support on this grim anniversary. but her father, former r&b star bobby brown, releasing an emotional reaction to those reports saying they're egregious, false, and will be dealt with at an appropriate time. bobbi kristina's aunt speaking out to fox adding that her condition is actually improving. >> she's opening her eyes. and there's a few more things that she's doing. krissy is doing well right now. >> that's sometimes almost a false message of hope. >> reporter: neurologist dr. john bookvar, who hasn't treated bobbi kristina, says in these cases even eye movements can be misleading. >> the eye opening in her case may completely be of a reflexive eye opening, one that means that she has improved to this persistent vegetative state, which is not a great end point. >> reporter: despite reports of diminished brain function, family and friends refuse to give up hope.

♪ and i ♪ >> reporter: kevin costner played opposite whitney houston in "the bodyguard" which featured her signature hit. ♪ i will always love you ♪ >> when we see bobbi kristina in peril we're wondering if you have any thoughts to share. >> she's sitting here fighting for her life surrounded by the people who love her the most. i think nobody wants more than her family, and if she could speak for herself, to have a second chance at this most precious life we're all given. i hope god opens her eyes and lets her breathe and lets her brain work and she gets a second chance. >> reporter: ever since whitney houston's untimely death bobbi kristina has publicly struggled with the loss of her mother. >> are you ready? >> reporter: the family allowed lifetime access to intimate moments in the months that followed, including bobbi kristina's first visit to her mother's grave site. >> the way she talked. the way she walked.

the way she smiled. i don't know why what happened happened. >> reporter: the cameras capturing 19-year-old bobbi kristina drinking alcohol. >> when i see krissy drinking i know that i'm not her mother but i have to look out for her. >> reporter: something that disturbed and worried her aunt. >> and this behavior -- is unacceptable. >> reporter: it's been 12 days since she was found facedown in a bathtub by her boyfriend nick gordon and a friend, max groman. >> possible cardiac arrest. 21-year-old female in the bathtub, face-down. cpr in progress. she is gurgling at this time. >> reporter: since she was hospitalized questions have been popping up around gordon, the man bobbi kristina described as her husband, a man who for a time was raised like her stepbrother. today police confirming there is criminal investigation under way. >> that's the way police departments should conduct investigations, treat every death as suspicious until evidence proves otherwise. >> we were told initially she was found facedown in the tub. what does that tell you? >> that's a red flag. we have to know about positioning, where the body is, is she clothed? these are things we don't know

yet. >> reporter: with few details emerging from the investigation, questions continue to swirl about what actually happened to bobbi kristina that day. >> you have to look at the house, if there's anything knocked over, sign of a struggle. because if you are thinking that this is a criminal act, the criminal act might not have happened in the bathroom. it might have happened somewhere else in the house. >> reporter: there's renewed scrutiny over a 911 call made roughly a week before bobbi kristina was found unresponsive. neighbors then complaining about a domestic disturbance. >> just had a neighbor call and report there was people hitting each other, swinging, outside in front of their town homes. >> reporter: but when police arrived, they found nothing but an empty house. gordon also reportedly had a restraining order filed against him by whitney houston's sister-in-law, who's the executor of the $20 million estate bobbi kristina inherited. in court papers posted by radaronline gordon was accused of making threatening comments and posting photos of guns with

the intention of making her fearful for her personal safety. ♪ from the moment i saw you ♪ >> reporter: bobbi kristina wanted to follow in her mother's footsteps, singing one of whitney's early hits "i'm your baby tonight" in her lifetime reality series. ♪ but you got that magic boy that is making me fly ♪ >> reporter: it's a love of music we saw early. at 11 months old when bobbi kristina joined her mother onstage at the american music awards she couldn't resist the allure of the microphone. her family has been keeping vigil by her bedside as they wait, hope, and pray. telling "entertainment tonight" -- >> do you see a positive outcome? >> i do. because i know the power of god. i know what he can do. >> reporter: for "nightline," i'm juju chang in new york. coming up here on "nightline," how eddie redmayne went from rock-hard abs in "jupiter ascending" to a body wrecked by a.l.s. in "the theory of everything" and what happened

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he may not be a household name yet but eddie redmayne is considered a real contender for best actor.3qf

though to undergo four months of prep and physical transformation to play a man increasingly constrained in his own movement. six-packed from his previous shoot on "jupiter ascending," redmayne reconfigured his body. with a choreographer's help, he sought to capture hawking at each specific stage of his decades-long battle with a.l.s. >> my god, how does jane manage? >> i just needed to train my body in order to sustain the positions. i knew that some of the positions would be specific and contorted and not necessarily comfortable. >> reporter: knowing hawking's

intimate, complex relationship with his wife jane would form the backbone of the story -- >> we'll be together for as long as we've got. if that's not very long that's just how it is. >> reporter: he closely examined key pieces of evidence from the hawkings' lives, such as this wedding photo. >> you see that he's not only on the stick. he's hand is on top of jane's. you can see, if you look closely, he's putting a lot of weight into her, body weight. it's an investigation that you started literally analyzing the different muscles in his body and working out what his decline was. >> reporter: just getting facial expressions right required hours of study. >> i used to sit in front of a mirror -- there were moments where you're like, no, am i parodying? is this a horrible kind of -- is this verging on -- am i going to be offensive? >> everything all right? >> reporter: yet it was only days before "the theory of everything" shoot began redmayne met his icon, stephen hawking himself, for the first time.

>> i'm getting out of the car and going, why have you not thought what they're going to ask? the truth, what did i want when i was meeting him, was approval. he was incredibly kind to me. >> reporter: redmayne's command of hawking's physicality lets viewers focus on the movie's emotional power. >> it's okay. it's okay, boy. >> reporter: with or without a win on oscar sunday, redmayne is doing what he loves. >> ever wondered, there's some other things i could do other than this? >> there absolutely are but i'm an addict for acting. >> reporter: i'm chris connelly for "nightline" in los angeles. ky