It was 3 a.m. on Dec. 31, 2017, when Matthew Riehl made his first 911 call from his home in Colorado's Copper Canyon apartment complex.
"This guy invited me to his house to kind of move in and he totally freaked out on me. He kept coming at me. I feared for my health and my safety," he said to the operator.
He also livestreamed his conversation.
Shortly after, a team of three officers lead by Deputy Zackari Parrish from the Douglas County Sheriff's Office were dispatched to check in on Riehl.
"There was a hazard hit on the home, saying that Matthew Riehl was a veteran with PTSD (post-traumatic stress disorder) and possible access to weapons," Deputy Taylor Davis told ABC News' "Nightline."
The events of that fateful morning would result in Riehl, 37, who was armed with nearly a dozen firearms, ambushing the officers, wounding three of them and killing 29-year-old Parrish.
A Castle Rock Police Department SWAT Officer, 41-year-old Thomas O’Donnell, was also shot and wounded.
"The suspect fired, I think, about 395 rounds at us and at other apartments," Sheriff Tony Spurlock told "Nightline."
The incident sparked a debate on stricter gun laws in the state, which recently rejected a law that would keep guns out of the hands of people with mental illness.
"Nightline" spoke to the responding officers about their slain colleague and what happened that day through their eyes.
When officers first arrived on the scene at Riehl's apartment, "It was fairly calm at that point," Davis said. "I believe [the call] was aired as a disturbance between two roommates."
First, Parrish split up the two men, Riehl and his roommate Matthew Thompson, and asked Thompson some questions.
"Why is he [Riehl] upset? … Is he on anything? Does he have any mental disabilities?" Parrish says to Thompson in bodycam footage.
"Not that I know of," Thompson says.
In the bodycam footage, Parrish tells Thompson that he is going to record his name and then leave.
Meanwhile, a different bodycam captured Riehl getting into an argument with Cpl. Coleman for refusing to give his ID. Footage from the officer's bodycam showed Riehl screaming, "Assault! Assault!" and "Liar!"
Deputy Parrish stepped in and calmed Riehl down.
"Zack immediately developed a decent rapport with him [Riehl]," Davis said. "Got him to calm down. Zack's approach to everything was very level-headed, very calm."
Because no crime had been committed, the officers left the scene soon after.
"We knew the roommate was going to work," Davis continued. "And we knew Matthew Riehl was going back upstairs to his room and then we were just going to move onto the next call and that was just it."
Roughly two hours later, at 5:14 a.m., Riehl made his second 911 call.
"The way he was talking to dispatch -- he was irate, he was amped and he was, you know, nonsensical," Deputy Michael Doyle said to "Nightline."
When the officers arrived, Parrish knocked on the door and kept repeating to Riehl, who was inside, "It's Zack. It's Zack. It's Zack."
After he told Parrish that he didn’t have any guns, Riehl opened the door.
"I noticed he's [Riehl] filming us. We get filmed a lot so I didn't really think much of it," Davis said.
The officers said Riehl told them he wanted to file a "domestic restraining order."
Then Davis said: "And then, I don't know, something switched and he just slammed the door in our face."
Riehl started yelling. At one point, Parrish mentioned an "M1 hold," referring to the mental health hold that law enforcement is authorized to do for 72 hours, even involuntarily, if they perceive a person is exhibiting behavior in which they might be dangerous to themselves or others.
Parrish and Davis linked up with Sgt. Dave Beyer, Deputy Michael Doyle and Deputy Jeff Pelle to help remove Riehl from his apartment. A game plan was chalked out.
"We had designated roles so everybody knows what they're doing when they're going into the scene," Beyer said. "[We were going to] put him in protective custody and get him to a mental health facility."
Davis was in front with the shield, officers said.
"Zack was behind me with his gun out for lethal coverage. Doyle was behind Zack with his stun gun out for less lethal. And then Sarge [Beyer] and Pelle were behind them, hands free," Davis said.
"Then we could actually go hands on and try to put him into custody and that was part of the plan," Beyer said.
As the team entered the apartment, however, they discovered that Riehl had trashed it and barricaded himself in his bedroom.
"It was like a hoarder's place," Beyer said. "There was all sorts of objects, debris scattered throughout the floor, throughout the apartment. He had not only just barricaded the door, but the entryway, with large objects that were designed to hang us up."
Parrish and Davis asked Riehl to come out.
"Zack pretty much whispered to me, 'Let's go ahead and kick the door 'cause he's not coming out,'" Davis said.
Little did the officers know that Riehl was waiting for them with a loaded AR-15 rifle. He fired several gun shots at them.
"I remember kind of wincing and turning sideways. And I'm, like, 'What's going?' Like, thinking, 'What's going on?'" Doyle said. "I remember thinking, 'Oh, he's actually, he's shooting at us.'"
Beyer estimated that Riehl probably fired a 30-round magazine on them within a few seconds. Parrish was shot.
"I hear Zack say, 'I'm shot, I'm bleeding out,'" Doyle said. "And so I look to my left and I see Zack's down. And my first thought is, 'My friend's down. I need to go get him.'"
Deputy Pelle said he grabbed his gun and stood over the top of Doyle, who was crawling on the ground and could only see Parrish from waist down.
"I just grabbed. I believe it was his right boot. And I just pulled as hard as I could," Doyle said. "I moved him probably two, three feet."
And, that's when the next round of bullets were fired. This time, Pelle was struck.
"The bullet entered just over my vest, just under my armpit," he said.
Doyle too saw blood coming out of his own sleeve but he kept his focus on his injured colleague, telling him, "You'll be OK. Stay with me, Pelle. Stay with me! Stay with me, Pelle. Stay with me."
Beyer started administering aid to Doyle, who in turn was helping Pelle. At that point, they said, it struck them that Davis was missing.
"We didn't know where she was but at that point, that's when I could tell I'm not good. Like, my lung collapsed. I was gargling blood," Pelle said.
Then Riehl started shooting again.
"I knew she [Davis] was in the apartment by herself, outgunned, in a strange territory," Beyer said.
"I ran into the roommate's room just looking for some kind of concealment, kind of preparing myself to get into a gun battle at this point with Matthew Riehl," Davis said. "Once I was inside that bedroom, I saw a window and I didn't have this thought process consciously, but I think my body knew that, you know, odds of survival inside the apartment were not great. Going out the window were my best odds. So I broke the window and then proceeded to jump out of it."
Davis broke a window, leaving shattered glass everywhere, her bodycam footage showed. One of Riehl's bullets hit her.
As Beyer yelled out to the officers, asking them to move, an injured Davis approached the group.
"That was one of the best things I've seen, is her running up, saying: 'It's Taylor,'" Pelle said.
That moment of relief quickly faded into horror, however, when the officers realized that Parrish was still inside.
"The moment when you realize Zack is inside and he's trapped. ... We're not the people who are supposed to feel helpless. And in that moment, you just, you felt really helpless," Davis said. "That was definitely one of the worst moments."
Davis called out for medical assistance on the radio.
"There's no messing around here,” she said. “Zack was inside and that I'm not hearing anything from him, and the shooting was still happening."
Under the hail of gunfire, the officers were forced to retreat without Parrish. Deeply concerned for another wounded officer, the officers turned their attention to Pelle, who had been shot in the chest.
Beyer, who was trained in officer's rescue because of his SWAT background, spearheaded the evacuation effort.
The fire department arrived, putting Pelle on a stretcher, and Beyer called Pelle's wife.
“She had to know,” Beyer said. “She know that—I have preach[ed] it to the team… that we all go home in one piece.”
Then Beyer then made an attempt to get Parrish out. "There was a chance he was still alive and for every minute that went by, his chance of survival decreased," he said.
Beyer said he headed back to Riehl's apartment with two additional deputies and SWAT teams who had arrived. As they approached the door, he said, Riehl attacked them with heavy gunfire, which continued for more than an hour and a half.
"He had an external camera," said Sheriff Tony Spurlock, who had arrived on the scene later. "He was extremely aggressive. ... He was firing multiple guns at the same time."
Riehl, who was recording the carnage on camera, amped up his attack every time he saw the officers approach the stairwell, Spurlock said.
"We had about 50 officers that were surrounding that apartment and trying to get into other apartments and situating themselves to where they could try to get some way into that apartment to rescue Zack," Spurlock said. "The suspect fired, I think, about 395 rounds at us and at other apartments."
Riehl had 11 firearms, he said, making it possible for him to keep up his attack for a long time.
Eventually, law enforcement used an armored vehicle to get better positioning and fired into Riehl's bedroom. Then, the SWAT team moved in.
"The SWAT team made entry into the front door," Spurlock said. "They rescued Zack and then in the process of doing so, they engaged the suspect. He fired on our officers and we fired and killed him."
The officers carried Parrish's body out and put it into the back of a truck.
At the hospital, the injured officers -- Doyle, Davis and Pelle -- learned that Parrish had died. It was a deeply emotional moment for them.
"He was alone in that apartment. He died there alone. I'll never get relief for that," Doyle said. "Even though I know I would have been killed, at least he wouldn't have been alone if I would have stayed in there with him. That's what haunts me."
At Parrish's funeral, his wife, Grace Parrish, gave a moving eulogy about her husband of 10 years and the father of her two daughters.
"I want them to know him as the amazing father and husband that he was. But, I also want them to know his passion for his career and desire to serve and protect," she said. "If you had told that team, someone is going to die tonight, Zack would have said, 'I'm still going in there. I will put my life on the line.'"
Four months after his death, little is known about Matthew Riehl’s possible motive except that he had contempt for law enforcement. Riehl's YouTube page is filled with anti-law enforcement posts, some specifically calling out Spurlock.
Riehl's long history of mental illness included suffering from psychotic episodes and an escape from a mental hospital. His mother had even called the police on him in the past.
In his mission to prevent an incident like this from happening again, Spurlock has been evangelizing the “red flag” gun bill, a measure that would give law enforcement and family members the option to petition the state court for a protection order that would allow firearms to be temporarily taken away from people considered a "significant risk" to themselves or others.
"This is not an attack on the Second Amendment," he said. "This is focusing on what we know as experts in the field, what has caused so many deaths. And it's people with a mental health crisis not being taken care of, not being provided treatment or care, and then having direct access to weapons, which they generally use on themselves, which is a tragedy."
But the “red flag” bill failed to pass in the Colorado state legislature last week.
Spurlock remains undeterred.
"I'm going to be a continued driving force to focus on mental health and I thought I made it very clear to the senators and the representatives of Colorado. Sheriff Spurlock's not going away," he said, adding that he believes the law would have prevented Riehl from buying the two rifles that he used in his attack against the officers and might have saved Parrish.
"I know for a fact this guy would not have been able to buy the two rifles that he used to shoot Zack and to continue to shoot our officers with," he said. “Now, surely he might have been able to get another gun, but it's much harder to get a black market gun than it is to buy a real gun.”
The incident has forever changed the Douglas County Sheriff’s Office, whose officers remember Parrish as a hero.
"Zack is downright a hero. There’s no other way about it. He's the poster child for who you want to hire as a police officer, who you want as serving your community," Pelle said. "That's what Zack was."