A federal law enforcement official said Ebel had been a member of the 211s, a white supremacist prison gang in Colorado. El Paso County sheriff's spokesman Lt. Jeff Kramer said Monday that investigators are trying to determine whether there was any gang involvement in the killing, but he stressed that's only one aspect of a broad investigation.
Denver police say Ebel is also a suspect in the March 17 slaying of pizza delivery man Nathan Leon.
Hickenlooper is a longtime friend of the suspect's father, attorney Jack Ebel, who testified two years ago before state lawmakers that solitary confinement was destroying his son's psyche.
Hickenlooper confirmed he mentioned the case to Clements as an example of why the prison system needed reform before the job was offered, but the governor said he did not mention Evan Ebel by name.
There was no indication that Hickenlooper's relationship with Jack Ebel played a role in the shooting. Hickenlooper said he did not having any role in Evan Ebel's parole in January.
Jack Ebel issued a statement offering condolences to all those who have suffered from his son's actions.
Clements, born in St. Louis, worked for 31 years in the Missouri Department of Corrections, both in prison and as a parole officer, before taking the top corrections' job in Colorado just over two years ago. He began a review of the state's solitary confinement system and eventually reduced the number of prisoners being held in solitary. He closed a new prison built specifically to hold such prisoners - Colorado State Penitentiary II.
His work won praise from groups including the American Civil Liberties Union and the union representing prison workers, which called him a "leader who looked out for those he led."
Officials took additional security measures after Clements' death and placed the state prisons on lockdown Friday.
Following Clements' killing, corrections professionals said their jobs have grown more dangerous for themselves and their families because of the growing influence of prison gangs, their ability to communicate with affiliates on the outside through smuggled cellphones and the ease with which people can be found and tracked online.
Clements is at least the second head of a state prison system to be killed. The top administrator of the Oregon Department of Corrections, Michael Francke, was stabbed to death outside his office in 1989 in what prosecutors described as a bungled car burglary. A former state prison inmate was found guilty of aggravated murder in 1991 and sentenced to life in prison.