this is "nightline." >> tonight, self-defense or murder? >> this is obviously no whodunit, it's a whydunit? >> a woman behind bars for killing the father of her children after allegedly enduring years of abuse. >> what were you afraid of? >> i was afraid he was going to kill me. >> nicky yatamando speaking from prison in an exclusive interview. >> i wish every day it ended differently. it was kill or be killed. >> prosecutors say she's a cold-blooded killer. >> the prosecution case was vicki was a master manipulator. night.t she says happened that - plus, fight for freedom. the case putting a spotlight on

how the criminal why is advertise system treats come bus survivors. >> we don't understand the psychological war fir that has happened to victims. >> the push for clemency. >> when you daydream about leaving this place, what does that look like to you? >> what happens now? find your beat your moment of calm find your potential then own it support your immune system with a potent blend of nutrients and emerge your best every day with emergen-c i'm feeling better. body pain? headache? nope. all in one and done. cuh-congestion? better. cough? fever? better. mucinex all in one relieves 9 symptoms in 1 dose. it's not cold and flu season. it's always comeback season.

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good evening. thank you for joining us. i'm trevor ault. tonight, nikki addimando speaks out in an exclusive interview from behind bars. why she says she killed her partner, the father of her two young children. advocates calling for clemency, saying her case is a chilling example of how domestic violence survivors are criminalized for defending their lives. here's my "nightline" coanchor juju chang. >> you've got violent encounter, man inside an apartment, and gun. >> how many shots were fired? >> one. >> this appears to be murder. >> there's just so many questions that are left unanswered. ♪ >> nikki and chris met pretty innocently. >> he started working at the gym she worked at. and it started as a friendship, and it developed into something romantic. >> nikki was more the kind,

compassionate, mothery side of taking care of the girls. chris was more kind of the goofy, joking aroundwith the girls. >> chris and nik led in n bout manhattan. far enough away so it doesn't feel like new york city, but it's not rural either. nikki gets pregnant. she and her partner, chris, move in together. a couple of years later welcome a second child. >> it looked like they had this beautiful life. for many reasons, we know that they didn't. it's the night of leading into the early morning september 28th. >> a vehicle at a traffic light, it's not moving. a police car pulls up behind her, nikki exits the vehicle. she's got no shoes on, she's visibly upset and shaking. >> one more time, go through the story with me.

is there anybody else in the house actually? >> no. >> she starts spilling this confusing, disjointed story. >> you have no idea why he might have the gun? how many shots were fired? >> one. >> okay, relax. >> he reached into the couch, and i meet him, and it fell. he said, "i will kill you and kill myself and the kids will have nobody." >> this is all happening in a small area. nikki at a traffic stop with officers about a half mile from the house where officers are now responding and the police station is just a mile away. >> they find a male laying on the couch, on his back. and this is chris grover. and he suffered one fatal gunshot wound to the left side of his head. there's a gun laying on the ground. >> reporter: after nearly two hours talking to police at that

traffic stop, nikki's taken into custody for questioning. >> i would like to hear your side of the story. >> they gave her every opportunity to explain this. from the officers at the scene, the story she tells them makes no sense. >> today, cps came because there was a report that i've been seen with bruises for a long time. >> nikki starts telling detectives earlier that same day, child protective services had visited their home to investigate claims made by an anonymous caller. >> reporting that they had seen her injured and they were worried about abuse at the home. >> nikki says she lied to cps, there was violence in her home. she says she was afraid that if she told the truth to cps, it would infuriate chris, a man she already feared. nikki detailing the moments that she said led to her fatally shooting chris. >> he pulled it out from there.

and i jumped up, and i kneed -- like not hard but kneed him a little bit and he flinched and dropped it and turned back over to me and said, "you don't have it in you, you're going to give me the gun and i'm going to kill both of us and your kids will have no one." and i just -- >> pulled the trigger? then what did you do after that? >> oh, god. t was loud. i don't know what to do. i didn't check his pulse, i didn't see anything but blood, and i left. >> that would, in the minds of law enforcement, not be consistent with somebody who's just had to defend their life. >> obviously self-defense, right? >> i mean -- i can't make that determination right now. >> she's raising this issue of self-defense during the interview. to investigators, this does not appear to be self-defense, this appears to be murder.

>> nikki's story of that night is bizarre but consistent. she says there was a history of abuse, that she wanted to leave but that chris wouldn't let her. so police are now wondering, this is a woman fleeing abuse? or fleeing the scene of the crime? >> the crime scene seemed to not quite make sense. there didn't look like there had been this struggle. >> for investigators, it doesn't make sense. they're fighting and they're struggling over a gun, yet he's on his back. >> investigators are developing a theory that nikki shot him while he was sleeping because the medical examiner rules that it's a hard contact wound. >> which means she actually put the gun to the side of his head and made contact with it when she pulled the trigger. >> when forensics searches the couple's phones, a few things stand out. >> five weeks prior to the murder, nikki sent a text where she references killing chris. >> in one text exchange with a

friend, nikki writes, "i have vent figured out how to kill him without being caught so i'm still here." then this emoji. >> that text exchange is not great for nikki's story of self-defense. but then investigators find something on chris' phone from the night of his death that they say is even more suspicious. >> shortly after 11:00, somebody is looking at and trying to get information about, what happens when you shoot a sleeping person? >> there's two possibilities here. either chris was searching for information on how to kill nikki, or nikki did that search herself in orde to make it look like chris was going to kill her. >> nikki addimando has been arrested and charged with second-degree murder. she says she shot the father of her two children in self-defense. >> reporter: nikki's sister

michelle takes in the kids and files for custody. >> when the news hit, so many witnesses come forward and say, "oh, i saw her at the walmart, her arm in a sling." "i saw her with a bruise on her face." people didn't know what to do. >> at the gym i started noticing some things that just did not seem right. finger marks on her neck and bruises on her neck. parents talking that chris could never do anything like that, many parents saying, what is he doing to her? >> reporter: one concerned parent brings a very reluctant nikki to police. >> there's actually an investigating and a recorded interview. >> reporter: that day, nikki isn't able to bring herself to report chris. >> nikki was hopeful that, at some point he would just grow out of it or get bored of it and then stop. unfortunately, that's just not what tends to happen with domestic violence. >> nikki said time and time again, "no one will believe me, everyone loves chris."

the violence was escalating. she was coming in with more and more injuries. visible marks and bruising. marks on her wrists. clear strangulation marks on her neck. >> reporter: nikki's therapist convinces her to have her injuries photographed by a forensic nurse. >> nikki says chris burned her with a hot metal spoon for talking back to him in a disrespectful way. >> i did speak with dutchess county prosecutors about options and the evidence that we have, and it did seem like everybody wanted to help. but the roadblock we kept running into was, we can't do much unless nikki reports. >> when chris is found dead in 2017, the d.a.'s office of duchess county is already familiar with nikki's name because of these allegations of abuse from prior instances. so they recuse themselves and pass the case on to the d.a.'s office in putnam county.

>> the narrative was, well, nobody has this much documentation. this must have been manipulated. when we come back, was it self-defense? or cold, calculated murder? in our exclusive interview, hear from nikki addimando in her own words about what she says happened that fateful night. >> i wish every day that that night ended differently. but the truth is, in that moment, it was survival, kill or be killed. type 2 diabetes? discover the ozempic® tri-zone. in my ozempic® tri-zone, i lowered my a1c, cv risk, and lost some weight. in studies, the majority of people reached an a1c under 7 and maintained it. ozempic® lowers the risk of major cardiovascular events such as stroke, heart attack, or death in adults also with known heart disease. and you may lose weight. adults lost up to 14 pounds. ozempic® isn't for people with type 1 diabetes.

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>> reporter: in front of this packed courtroom, you have nikki and her lawyers and the prosecution team. >> the prosecution's case was that nikki was a master manipulator. >> and she made a cold, calculated decision to murder chris grover on the night of this incident. >> the pictures at trial that the prosecution put forward were of him in a tutu, being this playful, fun-loving person. >> so therefore, he could not have been an accuser, therefore, nikki could not have been abused. >> reporter: one of the prosecution's key pieces of evidence was that text message nikki sent her friend five weeks before she shot chris. >> next for prosecutors, those deleted internet searches on chris' phone from the night he died. >> the prosecution contended very forcefully that nikki addimando was the one actually doing the internet searches. >> there was no evidence of any

connection, of dna or anything else of nikki on that phone. >> the prosecutors also pointed to the medical examiner's report that suggested that chris was shot at close range. >> in the medical examiner's report, you see the phrase "contact wound" which from the prosecution standpoint is consistent with chris grover being asleep on the couch. >> but the dutchess county medical examiner conceded during the trial that there was no way for her to conclude whether mr. grover was asleep at the time. >> reporter: in an exclusive prison interview, nikki addimando sits down with us and tells her side of the story. what made you want to testify in the trial? >> silence didn't serve me well. and it was time to speak. i had to. the truth is worth fighting for. >> we had medical professionals who testified to the actual physical injuries to her body

that really can't be contradicted. >> the prosecution's point of view is, what you're seeing in these photographs is self-inflicted, or it's from accidents that had nothing to do with chris grover. >> reporter: but when it's the defense's turn to make their case, they offer evidence that they believe helps to explain why nikki pulled the trigger that night. >> this was more than a murder trial. and if you did not look at it through a lens of understanding domestic violence, you would get it wrong. we don't understand the psychological warfare that has happened to victims. >> on the stand, nikki testifies that in 2015, two years before chris is found dead, she made a stunning discovery. >> reporter: according to nikki, chris had been recording the physical and sexual abuse, allegedly posting the images on a porn site. >> you described that to your therapist as a breaking point? >> i knew i should leave.

to have it filmed and broadcast -- it just brought a whole new level of shame and -- it was painful. >> reporter: but at trial, the question becomes, who posted those images? chris isn't visible in any of the photos or videos. and neither the prosecution nor the defense is able to directly link the account to chris. >> the jurors do see those graphic images of nikki. to counter that, the prosecution strategy is to say, well, maybe it's consensual. >> reporter: in addition to telling jurors about the years of abuse she says she endured, nikki needs to convince them that on the night in question, she believes she had no choice but to do what she did. >> would the jury believe that? >> reporter: the jury came back and found addimando guilty of second-degree murder and possession of a weapon. >> for nikki, it was the worst possible verdict. >> the jury came back and vindicated chris, and they

vindicated the family. >> justice served. here's his ashes. >> reporter: but around the time of nikki's conviction, a new law is enacted in new york state, the domestic violence survivors justice act. it gives courts the discretion to shorten sentences if survivors could prove that abuse was a contributing factor to a crime. >> the act was made for cases just like nikki's. it's clear that the abuse was a material cause of the crime for which she was convicted. >> reporter: but the court found nikki didn't qualify. >> the court was unconvinced by nikki addimando's contentions that chris was abusing her. sentenced to 19 years to life in new york state prison. >> part of the judge's reasoning is nikki, to his mind, had "a tremendous amount of advice, assistance, support, and opportunities to escape her alleged abusive situation." >> when somebody said, why didn't you leave?

what do you say? >> i was scared what would happen after that. i was scared to die and leave my kids without me. i also thought that i could make him happy, it would stop. >> reporter: just over a year later, later, addimaed a dough's case heard by an appellate court. >> this is a very sad and tragic historical narrative. >> the court of appeals did not have too much difficulty in unanimously concluding that the nature and extent of the abuse was not undetermined. >> reporter: nikki's sentence goes from 19 years to life, down to 7 1/2. as of now, she's served six years of that. >> they did reduce her sentence. but they did not reverse her murder conviction. >> reporter: we reached out to chris grover's family, and

although they declined to do an interview, his mother gail shared this with us. "we were very happy with the prosecution in this case and believe the jurors reached the right verdict. the appellate court's decision was a slap in the face. we believe nikki's accusations of abuse are untrue and maintain chris was a peaceful, loving partner and father." instead of getting out when her kids are young adults, nikki is now set to be released in 2024. >> thank you so much for being here. >> reporter: nikki's supporters now have a renewed mission, to get her home even before that new release date. there's only one person who can make that happen, the governor of new york, kathy hochul. stay with us. still disrupts my skin. severe eczema despite treatment it disrupts my skin with itch. it disrupts my skin with rash. but now, i can disrupt eczema with rinvoq.

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♪ nikki's file is one of so many sitting on the governor's desk. many of whom are domestic violence survivors. her application for clemency is still pending. but when the most recent list of names was announced last december, nikki addimando's was not among them. >> amongst the hundreds of letters of support that nikki has, there's one very loud letter saying the opposite. >> the district attorney wrote the following. "miss addimando was not the victim of sexual or physical abuse by christopher grover. to the contrary, she's a masterful manipulative who intentionally murdered chris grover in his sleep." >> when you daydream about leaving this place, what does that look like to you? >> just being with my kids. and helping them find normal for

our life. >> our thanks to juju. for more of nikki's story, stream the full episode of "20/20:kill or be killed" on hulu. if you or someone you know is in danger, there are hotlines including the national domestic violence hotline. 800-799-7233. these "nightline" for this evening. see you right back here at the same time on monday. thanks for staying up with us. good night, america.