Transcript for Family of Walter Wallace Jr. demand police reform
We want to turn now to another police-involved shooting death, Walter Wallace Jr. Was killed in Philadelphia. This has raised a lot of questions, and now his family is giving their first major interview to ABC's "Nightline." Here now "Nightline" anchor juju Chang. Reporter: Walter Wallace Jr. Was shot by police while in the midst of a mental health crisis. Walter's family had called 911 for help. Officers encountering Walter holding a knife. Don't shoot. Don't shoot. Back up. Reporter: Killed less than 60 seconds after police arrived. A marriage is a soul bond, when they took his life, my life was tooken too. Reporter: Walter's death became a rallying cry. Walter struggled with mental pillness. He was diagnosed with bipolar disorder. Some reports have shown people with untreated mental illness are 16 times more likely to be killed during a police encounter. After arriving, within 15 seconds you can clearly hear his wife shouting more than once, he's mental. He's mental. He's mental. He's mental. Put the knife down. When he shot him, he was going down, and he still was opening up on him. Reporter: Robert Gonzalez has spent his career studying these interactions after Eric Garner's death -- He doesn't lunge at the police officers. He's walking around, clearly he's agitated. Reporter: He says the problem with Walter's case began at the 911 call. It was the 911 dispatcher in my opinion who failed to ask the right questions so police could be armed with how to deal with this particular situation. Reporter: Philadelphia's police commissioner Danielle outlaw has built her career on reform. On this day she showed us her new crisis intervention training. So you reduce stress to take when you learned in the classroom into the real world. Yeah. Reporter: In this scenario, we watched police respond to a domestic dispute. What are you doing here? Get out of my house. Reporter: The man has a knife. Hey, hey, hey. Relax. Back up. Get out of here. Reporter: The police draw their weapons, but try to talk to him. They got all the information that he need and they communicated that over the radio, and what that does communicate as much information as they possibly can to allow additional backup to arrive. Reporter: Outlaw says reform is costly, but the family believes inaction costs even more. I cry every night. I cry every night. I regret myself. I should have jumped in front of him, and took the bullets. I mean, I just froze. Reporter: That moment haunts you? It will haunt me the rest of my life. Our thanks to juju Chang for that report.
This transcript has been automatically generated and may not be 100% accurate.