By Ashley Fantz
The investigation into the slaying of Colorado's prison chief has produced few clues.
Tom Clements was gunned down Tuesday night when he answered the door at his home in Monument, about 50 miles south of Denver.
"We are looking at all potential tips, leads, threats that Mr. Clements may have had from anybody in that prison system," El Paso County Undersheriff Paula Presley told CNN on Thursday. "The investigation is wide open at this point."
Asked whether the 58-year-old's killing might have been a professional hit, Presley replied, "We don't have any specific information that would lead us to that."
Clements was appointed to his job by Colorado Gov. John Hickenlooper, who signed landmark gun control bills Wednesday. Hickenlooper said that Clements was "supportive but not particularly active" in the measures, and it's unclear if that and his death are related.
As a precaution, Presley said, security has been beefed up Hickenlooper's office and other state offices.
Investigators are asking any witnesses to share information about a black, boxy-shaped vehicle that was seen running but with no one in it on Clements' street, Colonial Park Drive, around the time of the shooting. It might have been a Lincoln Continental or a Cadillac two-door.
Presley added a new detail about that clue: A man in the vehicle was seen driving away from the neighborhood about the time of the shooting.
Investigators are scouring databases to try to determine exactly what kind of car they're searching for.
At 8:37 p.m. Tuesday, a 911 call from a relative in Clements' house alerted authorities to the shooting.
Investigators are not releasing the name of the relative, but said the caller was the only other person home at the time.
Clements' death shook Hickenlooper, who spoke at an emotional news conference Wednesday.
He repeatedly praised the corrections chief, calling Clements a "dedicated, committed, funny, caring expert at corrections" who tried to ensure that prisoners had adequate support before their release.
"In many ways, Clements helped define what a public servant is," the governor said. "He did his job quietly and intently."
Hickenlooper appointed Clements as chief of the state's prison system in January 2011, according to Clements' online state biography. Before that post, he worked for 31 years in the Missouri Department of Corrections.
From October 2007 until January 2011, Clements was the director of adult institutions for the department, the biography says, overseeing 21 adult prisons.
-- CNN's Jim Spellman contributed to this report.