Story highlights Former school sent warnings about Riehl's online behavior

Suspect served in National Guard and Army Reserve, official says

(CNN) Just weeks before a barricaded man shot and killed a sheriff's deputy in a Colorado apartment, he apparently was writing alarming messages in email and on social media that included threats to police officers, officials have said.

Matthew Riehl, a 37-year-old former Army reservist, shot four sheriff's deputies who responded to a complaint at his apartment in the Denver suburb of Highlands Ranch on Sunday morning, killing one, police say. Riehl was killed during a subsequent shootout with a police tactical team -- a clash that also left a SWAT officer injured, authorities say.

The slain deputy was Zackari Parrish, a 29-year-old father of two. Two civilians outside the apartment also were shot and injured during the incidents, police say.

Police haven't revealed suspected motives for Sunday's shootings, but several law enforcement agencies had been aware weeks beforehand that Riehl was accused of writing harassing or suspicious messages online, officials said this week.

Douglas County Coroner confirms shooting suspect in #CopperCanyonOIS as Matthew Riehl DOB 9/09/80 (pictured). Investigation still ongoing and being investigated by @DA18th Critical Response Team. pic.twitter.com/H6wT0klSQv — DC Sheriff (@dcsheriff) January 1, 2018

That includes "harassing posts" that Riehl put on his social media sites in November about a traffic stop in the Denver suburb of Lone Tree, just a few miles east of his apartment in Highlands Ranch, said Lone Tree spokeswoman Denisse Coffman.

Read More