(CNN) -- The bullets that killed Colorado prison chief Tom Clements came from the gun found with a former inmate who died in a shootout with Texas police two days later, investigators confirmed Monday.
The news came as Colorado held a public memorial service for Clements, the executive director of the state Department of Corrections. The El Paso County, Colorado, Sheriff's Department said it was still trying to determine whether the suspect in Clements' slaying, Evan Ebel, acted alone or what his motive may have been.
"Tom Clements was a remarkable person," Colorado Gov. John Hickenlooper said. "He oversaw all of the coldest, darkest of worlds with the warmest and, you know, and most tender of hearts."
Clements was shot to death Tuesday night at his home outside Colorado Springs. Ebel was killed Thursday in northern Texas after a gunbattle with authorities that left a sheriff's deputy wounded.
The 28-year-old was a former white supremacist gang member and the son of a longtime friend of Hickenlooper. Police also said there is a "strong connection" between the killings of Clements and the killing of Nathan Collin Leon, a Denver pizza delivery driver who was found dead in suburban Golden.
Investigators said they have been looking into whether Ebel might have conspired with other inmates to kill Clements. The corrections chief earned widespread recognition not only for prison reforms but also for a crackdown on prison gangs, including the white supremacist 211s, who once counted Ebel among their ranks.
Ebel got out of prison in late January after serving seven years -- three for felony menacing, robbery and assault, another four for assaulting a guard. He spent five years of that time in solitary confinement.
It was his second stretch in prison, after doing one year of a three-year term for armed robbery.
Ebel's father, attorney and former oil executive Jack Ebel, "was one of my first friends in Colorado," Hickenlooper said. But the governor said Evan Ebel "had an anger and a cruelty" from an early age.
"He had a bad streak, and they tried everything," Hickenlooper said.
"One of the things Tom fought for was we have too many people in solitary confinement with mental disorders like Evan Ebel, and we release them -- we won't release them in prison, we release them into the general public," Hickenlooper said. It was a "quiet crusade" for Clements to identify and treat mental illness among prisoners, he said.
The governor said Clements' death was "incomprehensible, but I don't think it is part of a larger conspiracy."
The Texas Rangers said Ebel opened fire on sheriff's deputies northwest of Dallas on Thursday. He slammed the black Cadillac he was driving into a tractor-trailer, then crawled out and fired more shots at deputies before being shot in the head. The 9mm pistol and a Domino's Pizza uniform jacket and box carrier were found with the Cadillac.
Witnesses had reported a similar vehicle, -- a black, boxy car with Colorado license plates -- near Clements' home in Monument the day he was killed. Investigators had already said the brand and caliber of the shells found with the weapon were the same as those found at Clements' home.
CNN's Brooke Baldwin and Janet DiGiacomo contributed to this report.