Campus security's concerns were validated when Colorado authorities responded to a complaint of verbal disturbance at an apartment complex in Highlands Ranch, nearly 20 miles south of Denver.
The Douglas County Sheriff's department had been monitoring Riehl's YouTube page because he had been tagging them in his postings, officials said.
Authorities in Colorado say one deputy has died and four others were wounded, along with two civilians, in a shooting in suburban Denver. The four deputies, identified as Michael Doyle, Taylor Davis, Jeffery Pelle, and Tom O'Donnell too are stable.
Over 100 rounds were reportedly fired by the assailant, who remains unidentified at this time but was killed by police.
A law enforcement motorcade accompanied the fallen officer from a hospital in nearby Littleton to the coroner's office on Sunday.
He was also a veteran, who has exchanged angry tweets with the sheriff's office.
Parrish had been at the department about seven months and loved his job, Spurlock said. Police say he is survived by his wife and two children.
Following reports of shots fired, the sheriff's office issued a code red and instructed residents in the area to shelter in place.
Highway C-470 was closed due to the police activity and investigation and an emergency shelter was set up for people affected.
"They all went down within nearly seconds of each other so it was more of an ambush type of attack on our officers", Spurlock said.
Douglas County, Parker Police Department, Lone Tree Police Department, Castle Rock Police Department and Colorado State Patrol are on accident alert.
"I spent some time with his wife", said Sheriff Spurlock.
Just after 5 a.m., deputies responded to the incident at the Copper Canyon apartment complex located on County Line Road, between Colorado Boulevard and University Boulevard.
Vira Cover, 50, was still sleeping when her fiance called around 6:30 a.m. and told her to stay inside because of an active shooter in their apartment complex.
The Douglas County Sheriff (DSC) tweet about an officer down call.
President Donald Trump offered condolences on Twitter Sunday afternoon.
The officers were all shot and "went down within seconds of each other", but only four of them were able to "crawl to safety", Spurlock said.
Detectives at the University of Wyoming in Laramie said they called and warned police that suspect Matthew Edward Riehl had emailed threats against professors at the school - where he earned a law degree - and showed signs of mental illness.
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