Transcript for Former officer convicted of murder in wrong-apartment killing
For so many unarmed black and brown human beings all across America, this verdict today is for them! Everybody can raise their hands. This verdict is for them. This verdict is for them. We the jury, unanimously find the defendant, amber guyger, guilty of murders charged in the indictment. Reporter: Justice sometimes can feel elusive for mothers of black men. But for Alison Jean, her arms outstretched to the god she had prayed to on this day, justice had come. Amber guyger who killed Allison's son botham in his apartment was convicted of murder. For his family and the onlookers, this conviction represents something greater. This verdict is for trayvon martin, Michael Brown, Sandra bland, it's for tamir rice. It's for Eric Garner. It's for antwon rose. Today's victory gives a sense of hope and possibility and justice to the many people who were killed by the state and did not get any form of justice. Reporter: The verdict marking the climax of a case that's captivated the nation for more than a year. Breaking headline out of Dallas at this hour. The police call it a very unique case. Reporter: Fueling a national conversation about race, police transparency and one officer's use of deadly force. No justice, no peace! Reporter: Last September, amber guyger was returning home after a 13 1/2 hour shift. She lifted in 1378 on the third floor. Directly above her in 1478 was botham Jean's apartment. The St. Lucian described as a ray of sunshine. Botham had a love for everyone. Reporter: Jean was an accountant and an active member of the church of Christ. The spirit of the lord Reporter: That fateful night, he was home watching TV and eating ice cream. Guyger entered the apartment saying it was her own. This one stretched the imaginations and goodwill of even the most generous supporters of the police. The idea that someone could walk into an apartment that's not theirs, to somehow convince yourself that that person is in your house, committing a crime and your option is not to back out of house but to shoot and kill them, all those factors were incredibly hard to stomach. Reporter: Today's guilty verdict flies in the face of national trends surrounding police killings. 106 non-federal law enforcement officers have been arrested in conviction of shootings. Only four convicted of murder. In Dallas, some believe the tide is shifting. Amber guyger is the third officer to be convicted in recent years. Ladies and gentlemen, you have three innocent men. Reporter: The trend is in part due to reformers who campaigned on justice reform and supported calls for amber guyger to be charged with murder. Seemed to me people were misinterpret egg the case. This was murder based on the facts reported. Reporter: He made headlines, dismissing more than a thousand low-level drug cases before backing a bill requiring police to turn over all their evidence. Running on this platform of them going to prosecute police officers more and more. Reporter: During the trial, G guyger testified in front of a diverse jury, with five African-American jurors. She said she accidently parked on the fourth floor and walked in. She said she put the key in the door and it just opened. At that point she heard someone inside. I believed someone was moving around my apartment. I wanted to find that threat. Reporter: She says she saw a figure move toward her. In court, guyger demonstrated how she said she confronted the person. I had my gun pointed, and I'm saying let me see your hands, let me see your hands. What were you focussed on? Why did you fire? I was scared whoever was in my apartment was going to kill me, and I'm sorry. I have to live with that every single day. I'm an off-duty police officer, I shot a guy thinking it was my apartment. Reporter: Guyger's 911 call introduced as critical evidence. We have help on the way. I know, but I'm going to lose my job. I thought it was my apartment. Reporter: The Dallas county d.a.'s goal, pointing out contradictions in guyger's behavior, beginning with why she went into the apartment despite hearing noise inside. You could have called for help on your radio, and you could have had the Calvary there in two minutes. I could have. Could you have had S.W.A.T. Mobilized. I could have. And had you done any of those things, Mr. Jean would probably be alive today, right? Yes, sir. Reporter: Defense attorney Brian buckmire saying this was telling. When you look at the verdict that was given, murder, not manslaughter, it's obvious the jury believed in opening the door, pushing forward and knowing there were sounds someone inside that her actions inside that home were intentional and not reckless. Therefore, that was murder. When you aimed and pulled the trigger at Mr. Jean, shooting him in center mass, exactly where you are trained, you intended to kill Mr. Jean. I did. When your client is asked, did you intend to kill the person, your answer should be no, I intended to defend myself. Now if amber guyger taking the stand saying my intention was to kill him negates the whole, weren't you trying to defend yourself? Reporter: Last week, prosecutors played the chilling body cam footage. I thought it was my apartment! Reporter: Officers sprinting down a long hallway. You can see the bright red floor mat outside Jean's apartment, something prosecutors pointed out was something guyger should have noticed. On the body cam footage, several officers immediately start cpr trying desperately to save Jean. Something they say guyger did not do. Did you perform cpr on Mr. Jean? I did not. Why would you not try to do cpr? Reporter: She said she texted her partner and lover twice, telling him to come to the scene. Both of those times you put your needs and wants over his. I still cared about him. Reporter: While today's guilty verdict in the guyger case may have brought one city a step closer to holding police accountable, experts are still wary of any national shifts. It doesn't next the problem, and it doesn't erase the long history this country has of citizens dying and there being no justice. This jury had to make history in America today, because botham was the best that we had to offer. A 26-year-old college-educated black man. Certified public accountant, working for one of the big three accounting firms in the world, but it shouldn't take all of that. Right. For unarmed black and brown people in America to get justice. Reporter: For botham Jean's mother Alison it won't bring botham back. My life has not been the same. It has been a rollercoaster. I cannot sleep. I cannot eat. It's just been the most terrible time for me. Reporter: For "Nightline," I'm Marcus Moore in Dallas.
This transcript has been automatically generated and may not be 100% accurate.