victorious this is "nightline." >> tonight, apple versus the fbi. it is an abc news exclusive. one on one with company ceo tim cook. why he is refusing to comply with a federal demand to unlock the iphone of one of the san bernardino killers. >> this case is not about one phone. this case is about the future. >> how it feels to be in the eye of the storm in a fierce national debate over security versus privacy. >> it's not just about privacy, it's also about public safety. >> and what he has to say about donald trump's call to boycott apple. plus dalia dippolito made national headlines after she was accused of trying to have her now ex-husband killed in an alleged murder for fire plot. we're there in court as she finally takes the stand. and an emotional comeback

concert since the death of her husband. "with one more look at you." then the powerful encore.

it's dat bate pitting the fbi over apple. to be night apple ceo tim cook on why he is refusing to help the feds break into the phone used by the san bernardino gunman. "world news tonight" anchor david muir also gets cook to respond to calls by donald trump for an apple boycott. >> as we sit here you know some of the families of the victims in san bernardino have now come out in support of the judge's order that apple help the fbi unlock that iphone. one family reportedly saying, we're angry and confused as to why apple is refusing to do this. what would you say to those families tonight? >> they have our deepest sympathy. what they've been through, no one should have to go through. apple has cooperated with the fbi fully in this case. they came to us and asked us for all the information we had on this phone. and we gave everything that we had. but this case is not about one phone.

what is at stake here is can the government compel apple to write software that we believe would make hundreds of millions of customers vulnerable around the world, including the u.s.? >> and you'd have to write that system in order to unlock that phone? >> yes. the only way we know would be to write a piece of software that we view as sort of the software equivalent of cancer. we think it's bad news to write. we would never write it. we have never written it. and that is what is at stake here. >> the fbi though says it believes syed faruk used that phone to communicate with his wife, his accomplice. do you struggle at all with the possibility there could be information on that phone that could reveal other plots, other people involved in planning the san bernardino attack? >> david, if we knew a way to get the information on the phone that we haven't already given, if we knew a way to do this that would not expose hundreds of

issues, we would obviously do it. >> i want to get to what the fbi director james comey said. he said it's not about a slippery slope, it's about "14 people who were slaughtered and many more had their lives ruined. maybe the phone holds the clue to finding more terrorists, maybe it doesn't. but we can't look the survivors in the eye and ourselves if we don't follow any possible lead out there." do you understand where he's coming from? >> i do understand where he's coming from. and this is an incredibly complex issue. but it is about the future. think about this. if a court compels apple to write this piece of software, to place a back door in the iphone, we believe it does put hundreds of millions of customers at risk. >> reporter: we asked tim cook to explain this new system they would have to create to break into the iphone. >> the pass cord on the front like we all use to get into our iphones. after a certain number of tries it auto-erases?

us to develop a new operating system that takes out the security precautions, then they want a ability to go through a number of passwords at the speed of a modern computer. >> a computer would do that? >> a computer would do that. that is what they're asking for. we believe that is a very dangerous operating system. >> you hear that from the republican front-runner, donald trump -- >> what i think you ought to do is boycott apple until such time as they give that security number. >> is that the right route in saying boycott apple? >> the best thing is -- america's strongest when we all come together. >> is a boycott a way to come together? >> you know, i think a democracy is messy sometimes. but this -- i love democracy. that is who we are vinita nair. i think the best thing to do is to discuss and collaborate and work together on whatever the solution may be. >> let me ask you this.

the stories are legendary about new products with black drapery over them, locked doors, secrecy. any american company can keep a secret, it's apple. to those who might say, why didn't the fbi and apple team up far earlier in one of those secret labs and get this done and no one would have had to know about it? >> i can't talk about the tactics of the fbi. they've chosen what they've done. they've chosen to do this out in the public. for whatever reasons that they have. what we think at this point, given it is out in the public, is that we need to stand tall and stand tall on principle. there's probably more information about you on your phone than there is in your house. our smartphones are loaded with our intimate conversations, our financial data, our health records. they're also loaded with the location of our kids, in many cases. so it's not just about privacy, but it's also about public safety.

would set a precedent, if you didn't believe this would be a slippery slope, is this something your engineers could do and how quickly could they do it? >> we've never done it before so i don't know how long it would take. would i do it? in a perfect world where none of the implications that i'm talking about exist? yes, we would do it. we would obviously do it. but we don't live in a perfect world. >> in your quiet moments, do you have any concern about you might be able to prevent a terrorist attack by breaking into that phone? >> david, some things are hard. and some things are right. and some things are both. this is one of those things. >> in this case, you believe there are some things that just should never be created? >> correct. >> reporter: today steve jobs would have turned 61. cook says not a day goes by that he doesn't think about his iconic predecessor. >> have you thought about what he would have done in this situation?

and it is so clear to me that he loved what america was founded on so much and would do nothing to put all these customers at risk. he'd be doing the same thing. >> reporter: tim cook tells us they talked to the fbi early on, giving them advice, he says, on other ways to best get information from that iphone, to plug it in, to back it up to the icloud. >> did they do that? >> unfortunately, in the days, early days of the investigation, fbi directed the county to reset the icloud password. when that is done, the phone will no longer back up to the cloud. and so i wish they would have contact the us earlier so that that would not have been the case. >> how crucial was that missed opportunity? >> very crucial. the white house said this week that the fbi's request is "limited in scope." limited in scope, do you agree with that? and have you talked to the president on this? >> i have not talked to the president. i will talk to the president.

no. >> you have talked to the president before on these issues of privacy and security. >> yes. >> are you disappointed there wasn't more of a dialogue with the administration before this swift action from the justice department? >> yes. >> you wish there was more done? >> yes. i think there should have been. this filing -- we found out about the filing from the press. >> reporter: apple must respond to the court order by friday. >> i'm curious, tim. did you ever think that you'd find yourself at the center of such a crucial national debate? >> no. this is not a position that we would like to be in. it is a very uncomfortable position. to oppose your government on something doesn't feel good. and to oppose it on something where we are advocating for civil liberties, which they are supposed to protect, it is incredibly ironic. >> david, thank you for that exclusive report.

tonight a government official is telling abc news that it wants apple to be the only one who knows how they develop a new way into their phones, that the fbi doesn't want or need to know that secret. the debate continues. up next on "nightline," the woman at the center of a sensational case takes the stand. did dalia dippolito high to hire a hit man to hill her husband? celine dion singing all by hers in her first vegas concert since losing her husband. all by myself don't want to be all by myself anymore what if we did for mortgages what the internet did for buying music and plane tickets and shoes? you would turn an intimidating process into an easy one. you could get a mortgage on your phone. and if it could be that easy, wouldn't more people buy homes? and wouldn't those buyers need to fill their homes

with hand-lathed wooden legs? and wouldn't that mean all sorts of wooden leg-making opportunities for wooden leg makers? and wouldn't those new leg makers own phones from which they could quickly and easily secure mortgages of their own, further stoking demand for necessary household goods as our tidal wave of ownership floods the country with new homeowners, who now must own other things and isn't that the power of america itself now shrunk to fit the hands of a child, or, more helpfully, a home-buying adult. anyway. that's what we were thinking. with my moderate to severe ulcerative colitis, the possibility of a flare was almost always on my mind. thinking about what to avoid, where to go... and how to deal with my uc. to me, that was normal. until i talked to my doctor. she told me that humira helps people like me get uc under control

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it is the alleged murder for hire case that made national headlines. tonight the woman at the center of it, dalia dippolito, takes the stand with an unusual defense. here's abc ace linsey davis. >> i'm positive, like 5,000% sure. >> reporter: dalia dippolito, the woman caught on tape saying she was 5,000% sure she wanted a hit man to hill her husband, was back in court yesterday. taking the stand for the first time since her arrest in 2009 and her conviction in 2011 -- >> i have been accused of something that i didn't do. >> reporter: trying to explain away that incriminating video. her explanation? she was simply acting. >> this is supposed to be something you guys are going to put online so you can get publicity? >> on social media, right. so he can try to get an acting job from it.

part of a plan she hatched with her then husband michael dippolito and former lover to get famous. >> this is acting? >> yeah. >> reporter: prosecutors say that was no act. and allege she promised to pay this undercover cop posing as a hit man to kill her husband of six months. >> she parked the third space from here. >> you know, he gets two in the head. >> reporter: her now ex-husband mike dippolito said he couldn't wait to see what she said in court. >> let me know, i'll be sitting in the back with popcorn. >> walking on the sidewalk, this doesn't happen very often. >> no, it doesn't happen at all. >> reporter: in an exclusive pretrial interview with "20/20" this past december dalia dippolito said she's misunderstood. >> who is dalia dippolito? >> understanding, sweet, compassionate. >> because of that -- >> reporter: at the time her newly hired high-powered attorneys wouldn't let her talk about certain parts of the case, particularly those seemingly damning videotapes, because

after her first conviction was overturned on a technicality. but yesterday there was no avoiding them. she's forced to watch that moment we've all seen again and again. >> 5,000 percent sure. >> that's all mohammad told you to say, right? >> yes, he told me to say that. >> 5,000% sure? >> i needed to project confidence. and yeah. but that's what he told me, to make it look believable. >> reporter: perhaps the most surreal moment in the courtroom, when the prosecutor plays an audiotape of her trying to explain to her then-husband mike that she actually didn't pay to have him killed. >> please, i need an attorney, can you help me? it's not true. >> you said you wanted to have me killed, i heard that. >> it's not true, that is not true! >> reporter: according to her, mike was in on the performance from the beginning. so why, asks the prosecutor, is she trying so hard to convince him? >> you claim it was all made up,

how could that not be true? >> reporter: her attorney, brian claypool, says dalia is the innocent victim of a fame-hungry police department. >> this case is about a police department that tossed her under the bus for purposes of getting fame on a "cops" tv show. >> reporter: the now-infamous moment when police staged a fake crime scene and told dalia dippolito her husband was dead. >> is your husband michael? i'm sorry to tell you, ma'am, he's been killed. >> this special edition of "cops" is filmed on location -- >> reporter: he says it's all part of the plan so be on the reality tv show "cops" when mohammad came to them with the story about a beautiful woman wanting to have her husband killed. >> what the police department did is found out she's an attractive woman, in their minds they're like ching ching ching, this is a perfect skit to get on tape. >> reporter: not long after filming the exchange between the

posted the video online. >> why did you go back to the police department and immediately post, on youtube, a video of the staged crime scene of dalia dippolito? >> well, we posted it as part of our entire plan of publicizing the arrest in this case. >> you agree with me there's still a pending investigation on dalia dippolito and you posted the youtube video, right? >> yes. >> reporter: dalia's attorney says it adds up to only one conclusion, she was framed. >> there's no question about it, that the boynton beach police department was dead set on manufacturing a crime here. >> reporter: abc news senior legal correspondent sunny hostin says that remains to be seen. >> is this a case of entrapment? >> do i think that the police officers could have done better? yes. and you certainly don't as the police spokesperson upload that

is that a case killer? no. it isn't. >> seems unusual, correct me if i'm wrong, but for police to lie on camera and create a crime scene, make this elaborate circumstance to say, oh, your husband's dead, when he really isn't. >> that is unusual but not unheard of. i have to tell you that sting operations happen all the time. >> reporter: the boynton beach police department stands behind their investigation telling abc news -- >> the "cops" show happened to be here at the time of this investigation are we're not in the business of producing television. we're in business of saving lives and we believe we did that in this case. >> reporter: yesterday issuing a statement, we trust in our state attorney to successfully prosecute this case and we are confident we have given his office sufficient evidence to meet the state's burden. still, dalia's attorneys filed a motion to dismiss the case based on evidence of what they say is police misconduct. if the case isn't dismissed a

and there's one person who says he has no doubt dalia is guilty. kill me. >> reporter: for "nightline" i'm linsey davis in new york. >> thanks to linsey davis. you may have noticed sunny hostin providing legal analysis during that report. we would like to welcome her to abc news. she's joining us as senior legal correspondent and analyst. up next here, celine dion singing "all by myself" for the first time since the death of her husband. don't want to be all by myself dad, you can just drop me off right here. oh no, i'll take you up to the front of the school. that's where your friends are. seriously, it's, it's really fine. you don't want to be seen with your dad? no, it's..no.. oh, there's tracy. what! [ horn honking ] [ forward collision warning ] bye dad! it brakes when you don't. the newly redesigned volkswagen passat.

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finally, what happened when celine dion took the stage for the first time since the death of her husband? here's abc's deborah roberts. >> reporter: last night celine dion making an emotional return to the stage of the coliseum in las vegas. with one more look at you >> reporter: performing "with one more look at you," a poignant tribute to her late husband and manager rene angelil. >> every time i close my eyes, i felt rene on stage with me. he's always been on stage with me. and nothing will ever change that. >> reporter: it's been just a month since she lost her beloved husband to throat cancer. but there was never a question dion would return. "my career was in a way his masterpiece. the idea of leaving it unfinished would hurt him

all by myself >> reporter: a heartbreaking moment when dion broke into tears singing "all by myself." pausing to collect herself before powerfully finishing the set. i met dion last spring and though angelil was ill, he joined us on that very stage. despite it all, encouraging his wife to perform. >> sometimes, and i think i'm used to it, don't feel what you need to feel. just do it. >> go on stage? >> i did. because i love him. and i did. and it was very hard. >> reporter: now as a tribute to that love, celine singing once again. for "nightline," i'm deborah roberts in new york. >> our thanks to deborah roberts