A man suspected of shooting and killing an armed RTD transit security officer late Tuesday night was a former serviceman who was kicked out of a mosque in Texas, 9Wants to Know has learned.

The man, identified by Denver police as 37-year-old Joshua Cummings, had Islamic writings in his possession when he was arrested, according to sources with knowledge of the investigation.

Cummings was being held without bail on suspicion of first-degree murder. He is scheduled to appear in court Thursday afternoon.

RELATED: Attack on RTD security guard was ‘completely unprovoked’

In social media postings, Cummings identified himself as a jiu-jitsu instructor. He was active on Twitter in 2016.

“I seek refuge in the one God from the evils of Satan, and I begin in the Name of Allah, the Most Merciful, the …” he wrote in June 25, 2016.

“Wake up people. America is a failed state. It’s about to get so real. …” he posted on June 26, 2016.

And in a July 2, 2016, tweet, he called for a “former cop” in Arizona to be “put to death for treason”

Each of the posts had a link to a Facebook page that has been taken down, so it is not clear what the tweets referred to.

9Wants to Know spoke to a person who knew the suspected shooter. The person asked not to be identified because they said they were still afraid of Cummings. This person told 9Wants to Know, Cummings was “extremely violent,” and had “always been anti-cop.” In an interview, Cummings’ acquaintance told 9Wants to Know, “he (Cummings) held guns to people’s heads before. It didn’t surprise me he finally lost it.”

Tuesday night’s shooting baffled investigators, and numerous questions remain about his mental state. It's unclear that this 37-year-old man was doing in Denver, hundreds of miles away from his home in Texas.

The Denver medical examiner’s office identified the victim as Scott Von Lanken, 56, of Loveland.

Von Lanken was a contract worker for RTD from Allied Universal. According to Denver police, he was 56 years old and had a family.

Scott Von Lanken
Scott Von Lanken

According to an arrest warrant affidavit obtained by 9NEWS, two women approached Von Lanken just after 11 p.m. Tuesday to ask him whether they might be able to catch a light rail train. Just then, one of the women told police “she observed the suspect approach the victim from behind a place a gun near his neck.” The woman said “she heard the suspect say something to the effect of, ‘Do what you are told.’”

A moment later, the gunman fired, then ran off as the mortally wounded security officer crumpled to the ground.

Responding officers were searching the area when a security officer at a building at 1400 Wewatta St. told them there was surveillance video of the suspect leaving the area. After watching the video, the officers continued their search, locating the man about 11:50 p.m. on a patio of a complex at 1628 14th St.

They arrested Cummings there.

Sources tell 9Wants to Know Cummings had notes relating to Islam and a copy of The Quran. And as he was being arrested, he was praying on his knees.

According court documents, Cummings had a loaded 9mm pistol with him when he was arrested. Officers found a live round in the gun’s chamber and seven more live rounds in the magazine, which holds eight rounds. That ammunition was the same brand as a single shell casing found at the shooting scene, according to the documents.

Angela Burrell, public relations manager for Allied Universal, issued a statement about the shooting:

“Allied Universal is devastated by the loss of our valued security professional, a dedicated six-year employee, who was shot in the line of duty last night while proudly performing his duties in downtown Denver. We offer our deepest condolences to his family, friends and loved ones. The company intends to make a contribution in honor of the family to show our unwavering support. We ask that you join with us in keeping our fallen comrade’s family in your thoughts and prayers.”

Denver Police Chief Robert White said local authorities had no prior contact with Cummings and that his only criminal history was a misdemeanor charge in another state.

“We’re not 100 percent sure what motivated this particular individual to shoot the victim,” White said.

White said investigators were trying to determine if the security officer was shot because of his dark blue uniform, which resembles the one worn by DPD.

Barb Archer, the commander of the Denver Police Department’s Major Crimes Division, called the attack “completely unprovoked.”

Von Lanken died on the way to the hospital. He was one of 250 contract security officers employed by RTD.

Military records obtained by 9NEWS show that Cummings was in the U.S. Army from July 1997 through December 2002, where he was in the infantry and served on a mortar squad. He rose to the rank of sergeant.

During his time in the Army, he was stationed in Georgia, Louisiana, Germany and Texas.

After his active duty ended, he spent about 18 months in the U.S. Army Reserves.

Cummings was once charged with domestic violence in 2010 while living in Austin, Texas, but that case was dismissed.

9Wants to Know has learned he has a young wife who's in Denver too. Sources say investigators are talking with her.

Anyone who was in the area Tuesday night and may have seen something was asked to call Denver Police.