Joshua Cummings, was officially charged with the first-degree murder of Scott Von Lanken, a Denver Regional Transportation (DRT) security guard, on the morning of Feb. 3.
Commander Barb Archer of the Denver Police Department's major-crimes unit told CBS affiliate KCNC, "They [witnesses] saw a male approach the victim from behind, the male pointed a gun to the victims neck and then witnesses heard a gun shot, the victim fell, and the suspect ran off."
Cummings taught martial arts in Pampa and locals said his reputation varied, depending on who you spoke to.
Religious leaders told KFDA, Cummings would frequently visit churches trying to push his Islamic beliefs.
According to KCNC, the mosque he was affiliated with in Denver alerted Homeland Security about his suspicious behavior a month before the incident.
His behavior towards religious leaders, especially female pastors, along with a handful of suspect social media posts, led some people who knew Cummings to not be completely shocked when he made headlines.
"It was surprising to a point," said owner of martial arts dojo Peoples Kenpo, Alex Couch. "With his behavior the last few months here in town, it wasn't surprising. It was sad."
Others who took Cummings' martial arts classes said he was always respectful and never showed any signs of being radicalized.
"I never though he would do what he did," said former student Shiann Regalado. "I heard about it yesterday and so I wasn't too sure, my mom was saying that's him and I said no it's not. I was shocked about the whole thing."
Cummings is due in court March 3 for a preliminary hearing and is currently being held at the Denver Downtown Detention Center without bond and potentially without bail.