Transcript for Walter Wallace Jr. is killed by police less than a minute after they arrive: Part 1
I here now pronounce you husband and wife. You may kiss your wife, congratulations. Reporter: Dominique and Walter Wallace jr.'s wedding day last October sealed a love story years in the making. And you were pregnant at the time, how far along were you? Any day now. Reporter: Mr. And Mrs. Wallace were already parenting four kids together. What did you think your future was going to look like? Still being with our kids as a whole family. Happily ever after? Yeah. Reporter: Less than a month after wedded bliss, Walter Wallace Jr. Was shot by police while in the midst of a mental health crisis. Put the knife down now! Reporter: Walter's family had called 911 for help. Officers encountering Walter holding a knife. That's his mother frantically trying to protect her son. Ma'am, back off! Put the knife down! Reporter: Killed less than 60 seconds after police arrive. When they took his life, my life was tooken too. Say his name! Walter Wallace! Reporter: Walter's death became a rallying cry. Think about how a call for help ends up as part of a death sequence, is chilling. Reporter: Tonight we examine the intersection of policing and mental health with the Wallace family telling their full story for the first time. They murdered him. Reporter: And the Philadelphia police commissioner on what went wrong. Put the knife down! Reporter: In those 60 seconds. And what, if anything, can be done to fix the system. I have absolutely no issue withholding officers accountable and holding myself accountable. West philly is where you find generations of black working-class, working poor people. There's a long history of tension and violence between Philadelphia police and the black community. Reporter: West Philadelphia is where 27-year-old Walter Wallace Jr. Grew up. His dad, Walter Sr., a proud sanitation worker. His mom, Kathy, hands full with Walter and three siblings. What kind of son was he? A normal son, he was a pain in my behind a lot of times. I'm going to keep it real, know what I mean? Kathy, when you close your eyes, what memories of him come to mind? He sang rap. You got yours I got mine Reporter: Walter struggled with mental illness as early as 6 years old, eventually diagnosed with bipolar disorder. He was on lithium? Yes, adderall. 12, 13 different types of medicine. You'd been through the wringer? Yeah. Reporter: Walter's emotions they say sometimes led him to act out in violence ways. He'd faced trouble with the law, serving time in jail in 2017. His father says he was a devoted dad who after a series of odd jobs found steady work during the pandemic as a door dash driver. Walter's dream was to make it big with his music. We bros trying to get things right y'all Reporter: Ironically calling out policing and George Floyd's death in his song "Black heartache." A hard pill to swallow, you know what I mean? Thinking about my kids burying me, and I have to bury my kid. It's like -- like the devil's riding over your back. Reporter: It was a day brimming with hope for Dominique and Walter. I was supposed to give birth that day. That was your due date? Yeah. Reporter: Walter had gone to his parents' house after his car had gone missing days earlier, a devastating blow. He had gone around looking for his car, because that's where his income came from. Becaus he's a door dash driver, so he's lost his livelihood. Yeah. Reporter: When Dominique and Walter reported his car missing, she says the police laughed at them. Walter's family says he was triggered into a mental health crisis. Police, how may I help you? My brother, they called the cops earlier and the cops aren't doing nothing. Any weapons involved? No, but he on probation, he got a case for being violent, he got a whole record. We'll help them out, stay on line for medics, okay? We was arguing, not fighting. I was trying to chase them and I fell. Philadelphia police 074. My mom, my mom need help. Why were you chasing him? Sometime he acts real crazy at times, so I wanted to act up. He was on leave for psychiatric help. Reporter: His wife had been called to the house to help calm Walter home. I'm telling him, we need to go home, I don't want to deal with the police, you don't want to deal with the police. Reporter: They had reason to worry. Reports have shown people with untreated mental illness are 16 times more likely to be killed during a police encounter. Officers use caution responding, this is an ongoing domestic issue. What's going on? He came outside. He had the knife in his hand. Put the knife down now! Put the knife down now! Reporter: After arriving, within 15 seconds, you can clearly hear his wife shouting more than once, "He's mental." What were you trying to communicate to the officers? He needs help. In that moment, it just is like, y'all adding fuel to the fire. Back off, back off, back off! I grab him. But he swung me out of the way. Reporter: Not only were police body cams capturing the incident, neighbors were recording. Put the knife down! Did they spend a lot of time talking to him? No. Didn't say nothing. Then like, whoa! When they shot him, he was going down, they still was opening up on him, you know what I mean? And he just fell. That was it. He took his last breath. Reporter: Less than one minute after they arrived on scene, Walter Wallace Jr. Is dead. The two officers fired 14 rounds, 10 bullets striking Walter. They had it set in their mind to crucify my son. That's exactly what they did. You're supposed to come and help. Help didn't come like the help we needed. You killed my son! You killed my son! Stop, stop, back up -- You killed my son! Stop! What the hell y'all just do? My body going through shock. I'm shaking. Reporter: Robert Gonzales has spent his career studying these interactions, helping change training techniques at the NYPD after Eric Garner's death. He doesn't appear to be lunging at anyone. He doesn't lunge at the police officers. He's walking around, clearly he's agitated. Both officers are yelling at him to put down the knife. Reporter: Gonzales says the problem with Walter's case began at the 911 call. The systems the 911 dispatcher that the suspect has a record. Was it a criminal record? Was it a medical record? It was the 911 dispatcher, in my opinion, who failed to ask the right questions so that the police officers can be armed on how to deal with this particular situation. Put the knife down! Put the knife down! Reporter: In addition to being ill informed, the officers were ill equipped. In Philadelphia most officers are not issued less-lethal forms of force like a taser. Gonzales says the only option they could use to disarm him at that point was their gun. I believe when he failed to comply, after maybe the sixth or seventh attempt, they realized he was never going to drop the knife. Then you need to use deadly physical force. In my opinion, this was a just fight shooting. Me personally, I probably wouldn't have discharged my firearm. If the officers had continued to maintain the zone of safety, if they would have requested additional backup, where someone who responded might have had a taser, and then perhaps that would have saved a life in this situation. There are many things that made Walter Wallace more vulnerable to the type of violence he experienced. Being black does this. Being male does this. Struggling with mental illness does this. Living in a neighborhood that is considered high crime or high risk does this. Reporter: For the Wallace family, the pain is present in many ways. I cry every night. I cry every night without my son. I regret myself. I should have jumped in front of him, took the bullets, know what I mean? I froze. That moment haunts you? Haunt me the rest of my life. When we come back, tough questions for Philadelphia's police commissioner. When you look at that video, what went wrong that day? And we go inside a heated training session. Get out of my house! And the reforms that Walter Wallace jr.'s family demands.
This transcript has been automatically generated and may not be 100% accurate.