(CNN) -- The executive director of Colorado's prison system was shot as he opened his door, according to a 911 caller that police have identified as a relative in the home.

El Paso County sheriff's deputies arrived at Tom Clements' Black Forest home -- about 20 miles outside Colorado Springs -- to find the 58-year-old dead Tuesday night, said Lt. Jeff Kramer.

The 911 call came in at 8:37 p.m., Kramer said, but he would not identify the relative for reporters Wednesday. He said the relative was the only other person in Clements' home at the time of the shooting, and added that it's unclear whether that relative was in the same room as Clements or in another part of the house.

Kramer said that a boxy-shaped black car, possibly a 1990s model Lincoln, had been seen running with no one in it on Colonial Park Drive, the street where Clements lived. That vehicle, the sheriff's spokesman said, was driven away later in the night, though it's not clear what time.

Investigators worked the crime scene all night, collecting evidence, and are working Wednesday, canvassing the wooded property and talking to neighbors, Kramer said.

Asked about any suspects or a possible motive, Kramer said that authorities know that Clements' position with the prison system "opens a dynamic" in the investigation, meaning that someone related to the prisons may have wanted to harm him.

"We're sensitive to that," Kramer said, but he added that authorities are "remaining open-minded" about all angles.

Kramer said that investigators are "not aware of any threats" that Clements might have received before he was killed. Investigators have not been able to determine if the shooter got away on foot, in a vehicle or both, he said.

A canine unit was used Tuesday night, Kramer said.

"We just don't have" a description of anyone who might have been involved in the crime, Kramer told a reporter who asked if investigators had an idea of who the killer or killers were, but were choosing not to release that information.

Kramer said that if investigators had a description, they would release it because the public might be able to help authorities.

Gov. John Hickenlooper has ordered flags in the state lowered to half-staff from sunrise to sunset until after Clements' funeral. Arrangements are still being made.

The governor addressed reporters Wednesday morning, saying that he was hesitant to go into details about the case to make sure that he didn't hamper the investigation. He said he got a call around 9:30 p.m. Tuesday.

"It was a very long night," he said. "Tom Clements was such a remarkably talented individual" who was good at "getting things done and figuring out solutions."

"He was by nature a problem solver," he said.

Clements leaves a wife, Lisa, and two daughters, Rachel and Sara, the governor's office said.

Hickenlooper appointed Clements the 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.

Clements' shooting comes as Hickenlooper is expected Wednesday to sign landmark gun control bills. The new legislation includes a 15-round limit on magazines, universal background checks for prospective gun buyers and a requirement for gun purchasers to pay for their own background checks.

The legislation followed mass shootings, including one last July in Colorado, when a gunman at a movie theater in Aurora killed 12 people and wounded 58.

Asked whether Clements was "active" in his support for the new gun legislation, Hickenlooper, in an emotional Wednesday news conference, replied: "He was supportive but he wasn't particularly active."

The governor called Clements a "dedicated, committed, funny, caring expert at corrections" who tried to ensure that prisoners had adequate support before their release.

"In many ways, he helped define what a public servant is," Hickenlooper said. "He did his job quietly and intently."

CNN's Shawn Nottingham and Tina Burnside contributed to this report.