DOUGLAS COUNTY, Colo. — More details are emerging about the man who reportedly opened fire on five Douglas County officers in an ambush-style attack New Year's Eve.

Matthew Riehl, 37, was shot to death Sunday after shooting at the deputies, killing one.

The suspected shooter was an Iraq War veteran. He was deployed to Iraq in 2009 and was honorably discharged in 2012.

A spokesperson with the National Guard confirmed to Denver7 that Riehl entered into the United States Army Reserves in 2003 and served in the Wyoming National Guard.

While living in the state, it was revealed Monday that he was the subject of a warning to University of Wyoming students two months ago.

The Nov. 6 email from Assistant College of Law Dean Lindsay Hoyt told students to notify campus police if they saw Riehl or his vehicle near campus. The email included a photo of Riehl and his car.

UW spokesman Chad Baldwin said Monday that the school in Laramie, Wyoming, was investigating social media posts in which Riehl mentioned the College of Law and some of its employees. The vulgar, alarming posts did not contain any direct threats but did include pictures of Riehl holding a rifle.

Colorado authorities notified

University of Wyoming Police Chief Mike Samp told Denver7 they reached out to police in Colorado to share their concerns.

"We reached out to the front range trying to locate where Matthew Riehl was living," Samp said. "Former National Guard contacts helped us determine that he was living in Highlands Ranch, in the Lone Tree area."

Samp added, "We were certainly approaching it from a welfare check standpoint. The language in the posts did not rise to the level where we could take action criminally, by Wyoming state law, but we wanted to make sure the authorities in Colorado were aware of this individual and had all the information we had regarding him."

When asked about specific concerns, the chief replied, "He was prior military. We were highly suspicious that there were some mental health concerns. He obviously had access to weapons, as well as the language in the posts themselves certainly raised a lot of red flags for us. That's why we took the proactive steps we did with the College of Law."

Baldwin told Denver7 that Riehl graduated from the College of Law in 2010 and that he made the Honor Roll in 2007.

He also said that security on campus was increased for a short time until police determined that Riehl was in Colorado, not Wyoming.

Shooter was active on social media, streamed confrontation with police

Aside from his military history, he was also active on YouTube, posting several telling videos.

In a clip posted on the video-sharing website a few weeks ago, Riehl calls for the firing of Douglas County Sheriff Tony Spurlock and rails against him in highly personal terms.

In the same video, he is also seen holding up a deputy's business card and accusing the deputy of being a pimp.

"The pimp will then ambush you from behind the door," Riehl is heard saying in the video, which has since been removed from the site.

Denver7 has also learned that the shooter live-streamed his confrontation with deputies online on Periscope.

In a graphic audio and video clip, published on the website LiveLeak, Riehl can be heard yelling at first responders before opening fire.

The following transcript of the encounter, although a partial example of the recording, is graphic:

"Go away... go away... don't come in... I warned you," the voice yells, before loud shots can be heard.

"What? Get the f--k out of here! Why are you here? You don't have a warrant! Go away.... leave me alone... get out," before more shots.

The entire audio clip is only about a minute long.

Sources tell Denver7 Investigates that the shooter did live stream the incident, and that the video is being compared to officer body camera footage as part of the investigation.

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The Associated Press contributed to this report