A federal law enforcement official said Evan Ebel was a member of a white supremacist prison gang, the 211s. The official wasn't authorized to discuss the investigation publicly and spoke on condition of anonymity.
Colorado officials wouldn't confirm Ebel's membership but placed state prisons on lockdown Friday afternoon.
"There's been an inordinate amount of media attention on one threat group, and that has required additional security measures," Morgan said. The corrections department also was preparing for a Monday memorial service for Clements, she said.
The 211 gang is one of the most vicious white supremacist groups operating in the nation's prisons, comparable to the Aryan Brotherhood of Texas, according to the Southern Poverty Law Center, which tracks extremist groups.
Founded in 1995 to protect white prisoners from attacks, it operates only in Colorado and has anywhere from a couple hundred to 1,000 members, senior fellow Mark Potok said Friday.
Legal records show Ebel was convicted of several crimes in Colorado dating back to 2003.
Scott Robinson, a criminal defense attorney and media legal analyst, represented Ebel in 2003 and 2004. He said Ebel had been sentenced to a halfway house for a robbery charge in 2003 before he was accused in two additional robbery cases the following year that garnered prison sentences of three and eight years.
"I thought he was a young man who was redeemable, otherwise I wouldn't have taken the case," Robinson said, saying he didn't recall the details of the case.
Robinson said he knew Ebel before he got in trouble. He said Ebel had a younger sister who died in a car accident years ago.
Vicky Bankey said Ebel was in his teens when she lived across from him in suburban Denver until his father moved a couple of years ago. She remembers seeing Ebel once jump off the roof of his house. "He was a handful. I'd see him do some pretty crazy things," she said.
"He had a hair-trigger temper as a kid. But his dad was so nice," Bankey said.
Hickenlooper agreed that Evan Ebel had "a bad streak" that his parents had tried to correct.
"The events of the past few days have been devastating for all involved," he said in the written statement. "I am in shock and disbelief about how everything seems connected in this case. It makes no sense. Tom's death at the hands of someone hell-bent on causing evil was tragic in every way. It also now appears Tom's killer may have had another victim. Our hearts and prayers are with Nathan Leon's family as well."
Contributing to this report were Associated Press writers P. Solomon Banda, Dan Elliott, Colleen Slevin, Alexandra Tilsley and Catherine Tsai in Denver; Thomas Peipert in Colorado Springs, Colo.; and Angela K. Brown in Decatur, Texas.