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BOULDER, Colo. (KDVR) — It has been a little more than three months since a mass shooter in Boulder took the lives of 10 people.

While the suspect has been arrested and charged, the investigation is still ongoing. FOX31’s Deborah Takahara was invited to sit down with the four lead detectives on the case for an exclusive interview.

While they can’t discuss details of the case to protect the prosecution, they did want to share some insights into the work that has gone on behind the scenes and the impact it is having on them.

From the very beginning, they said this was a team effort. On March 22 at 1 p.m., when the suspect opened fire and calls of an active shooter went out, dozens of law enforcement agencies and other first responders rushed to the King Soopers on Table Mesa Drive.

“So we got called in on Monday, and the first thing I remember is getting there and everyone showed up,” said Detective Kevin Marples, fighting back tears. “Hundreds of first responders showed up to help where they could. To see Table Mesa lined with cop cars, because everyone wants to help, was a lot.”

These four detectives were not first on the scene, but they were tasked with piecing together what happened.

“Having the ability to work together as a team and coordinate different parts of what we’re going to do was helpful. It’s a lot, a lot to chew,” said Detective Keo Sidara.

They have spent hundreds of hours interviewing witnesses, analyzing every piece of evidence and reviewing hundreds of hours of surveillance video. They have reviewed 1,100 reports.

“A lot of it early on was trying to make sense of it and organize it,” Marples said. “How can we take everything that happened and everyone that showed up and start organizing it. Once we were able to do that, it made it easier.”

Marples, a six-year veteran of the Boulder Police Department, is leading the investigation.

“We had a running task list that would get assigned out. There would be no way for Boulder PD to do that on our own, even if you had every officer working it 24/7. It would never get done,” Marples said.

“It’s a process that continues to this day. Everyday, it’s something: a new report, someone needs to be interviewed. I mean here we are going on June, almost into July, and it’s still a daily process for all of us,” Marples said.

“Going through all the surveillance footage, I work this case as most of us do, every single day. Even on my days off, I’m working this case, so it never really gets a chance to go away. So some days are definitely easier to handle than others,” said Detective Sarah Cantu, who has been with the Boulder Police Department for 20 years.

To all of them, this is personal. Detective Heather Frey went to school at the University of Colorado Boulder and has worked for Boulder police for 20 years. This was the first time she has lost a colleague in the line of duty. Officer Eric Talley was killed responding to the shooting.

“This is our community, so it definitely hit home. We could see the impact it had on the city as a whole and the police department. What we had to think about, even though we were all grieving, that we had to think about what we needed to do as a team to be able to put forth the best case to the district attorney’s office to honor Eric and all the other victims of this tragedy,” Frey said.

This team has overcome incredible challenges with one thing in mind: justice for the victims.

“Just viewed that footage over and over and over again, which obviously wasn’t easy, but it allowed us to identify additional charges for our suspect. It also allowed us to identify additional victims. Many of them didn’t even realize they were victims, or at least to what extent,” Sidara said.

These detectives say the outpouring of support from the community has been a big part of this team effort and has motivated them to return day after day.

“The conclusion of this is a long way in the future, so it’s helpful for them to support us. We are part of the community. This impacted all of us, not just in this room, but in this building. And so we are hurting with them and we will heal with them,” Cantu said.

In the days and weeks that followed, these are the agencies that provided assistance: Bureau of Alcohol, Tobacco, Firearms and Explosives, Boulder County Sheriff’s Office, Boulder Incident Management Team, Boulder Office of Emergency Management, Colorado Bureau of Investigation, Colorado Department of Public Safety, Boulder Coroner, Colorado Organization of Victim Assistance, University of Colorado Police Department, District Attorney’s 20th, DA Investigator 20th, DA Investigator 18th, Employee Assistance Program, Federal Bureau of Investigation, Longmont PD, Mothers Against Drunk Driving, Boulder County Critical Incident Team, National Capital Region Homeland Security, Thornton PD, US Attorney’s Office, Westminster PD.

The investigation has taken an emotional toll on the investigators.

“What can happen in eight minutes is earth shattering,” Marples said. “For the first few weeks we worked nonstop. The first time it hit me was I finally had to go to the grocery store at home. I walked up to the grocery store and there was a plaque and table with candles. I just sort of had to leave.”

But he says they have found bright spots amid the horrific images they have had to watch repeatedly.

“What made it easier is as you kept watching, you got to see the good things people did from officers running in, from all these people responding who didn’t know us, to community members running back in the store to help people. It didn’t make it easier, but it was nice to see in chaos when everything was falling apart, the community came together to help everyone. It sort of made it doable to get through this. There is still good things happening. There are still good people and that’s what has made this bearable to get through,” Marples said.

These detectives are themselves part of the good. In addition to working around the clock on the investigation, this team took the time to painstakingly identify personal belongings and return them to their rightful owners.

“It was very eerie. You just saw shopping carts left in the middle of the store, you saw shopping carts left in places you wouldn’t see. Shopping carts normally aren’t back in the coolers. Looking at that and knowing someone was so terrified they were hiding in these coolers and just left all their belongings. We just knew we had to return their items to them. That was at least a little good feeling,“ Frey said.

“You walked through in the beginning, it was eerie in the beginning, because it was like everything just stopped. So there were phones off the hook, at the self-checkout there were people’s credit cards still in the machines, cash coming out of the machines. I remember looking at the self-checkout and seeing a wallet, ID card, social security card, just thinking how hard it must be now for these people. They went through all this and they think now I have to get a new social security card. So as a group we decided, why don’t we take what’s not evidence and team of us went back and picked up everything that wasn’t evidence and started linking it with people so we could at least give them something back,” Marples said.

Once the evidence collection was complete, they escorted other first responders back to the scene.

“We were able to take officers and first responders and allow them to walk through the scene after the FBI was completely finished processing it. We were able to let them walk through and process what happened, which I’ve never heard about that in my whole career here, to go back to a scene. Maybe just being there and seeing how it is now instead of in that chaos, I think that helped them immensely. I know it helped us,” Frey said.

“We had officers, dispatchers, coroner’s investigators, and we were able to work with victims’ advocates with organizations, how we should do this, bring people in and let them process what happened. Victim’s advocates there, service dogs, chaplains were there, anything we could to do to support trying to process the tragedy and what happened. I hope it helped them heal. I even think it helped us heal a bit by helping them, seeing what we could do. Not just with the case, but all the other little things we could do,” Frey said.

They say one of the highlights has been the community support, and specifically all the companion animals and therapy animals that have stopped by to lift their spirits.

It will take some time to heal, and even though these detectives have seen the worst of the worst, they say they would have it no other way.

“All the people we work with in this building, I consider them to be part of my family. So even during harsh times like this, difficult times like this, we get through it together. Then be able to give back to the community the way we do is extremely rewarding, and I wouldn’t change it,” Sidara said.

“As hard as it is, the tragedies we have to see and process, all of the other things outweigh that in terms of working with all my colleagues, from patrol officers, dispatchers, records, to my fellow detectives. That is the most rewarding thing I can imagine in a career,” Frey added.

“I wanted this case because this is something I can do. I wasn’t in the store, I wasn’t available when those officers ran in without thinking, I was a block away. That was the closest I got that day. So this is something I can do for the community, for our officers, to put together a case that is the best case possible. It’s something I can do to show my appreciation and just have a hand in it, to do something,” Cantu said.

For Marples, the time has come to move on. “This will be my last case. Last year, I decided to make a career change. For me, it’s been hard to see. In detectives, it’s always bad and I wanted to work on something that wasn’t that way all the time. I couldn’t think of a better honor than dedicating my last few months as an officer with this case,” Marples said. He will remain with Boulder PD, in the IT department.

Boulder Police Chief Maris Herold said this: “To say I’m beyond proud of these four detectives as well as every member of the Boulder Police Department would be an understatement. They have worked—and continue to work—tirelessly on this investigation to bring justice to the 10 lives taken on March 22. In my nearly 30 years in law enforcement, I’ve never seen such seamless cooperation among agencies and dedication to community transparency and engagement than I have with this investigation.”

These detectives spent between eight to nine days reviewing video evidence, which led to 115 charges against the suspect. They identified 16 civilian victims and 11 other uniformed personnel.