By Brian Maass

DENVER (CBS4) – The suspect arrested and suspected of shooting and killing an RTD security guard Tuesday night was found with what law enforcement sources describe as Muslim documents, according to multiple law enforcement contacts, and had been known to federal law enforcement.

Joshua Cummings, 37, a Texas native, was arrested shortly after the murder of RTD security guard Scott Von Lanken. Von Lanken worked for a company called Allied Universal, a security company contracted out by RTD.

Von Lanken was shot in the head by an assailant who fled. Police say they arrested Cummings soon after, not far from the shooting scene. They say they also recovered a gun.

Multiple law enforcement sources told CBS4 Investigator Brian Maass that Cummings had Muslim documents with him when he was arrested, and seemed to speak in an Arabic language following his capture.

Cummings owned a Jiu-Jitsu academy in Texas and in an online profile wrote:

“I prepare people for real world combat as they might experience if attacked one day on the street.”

Police say Von Lanken was talking to two women providing information about light rail service when the suspect approached him and shot him in the head.

Police said Von Lanken had a family but released few other details. Von Lanken was pronounced dead shortly after the gunfire.

CBS4 has learned that Cummings is originally from Texas, where he was arrested in 2010 for assault. He also has previous traffic stops in Oklahoma.

Cummings wrote that he worked in the oil business as a landman. Cummings reported that he also worked in private security in 2012 in Austin, Texas.

An acquaintance of Cummings told CBS4 “He creeped everybody out.”

“He was a crazy man,” said the acquaintance, who asked not to be identified.

The man told CBS4 Cummings was fired from his job working at a nightclub for assaulting a co-worker. He said a month ago Cummings returned to the bar to tell people “he was leaving for Denver.”

Statement From Allied Universal

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.

CBS4 Investigator Brian Maass has been with the station more than 30 years uncovering waste, fraud and corruption. Follow him on Twitter @Briancbs4.