El Paso County, Colorado (CNN) -- A man who dedicated his career to working in the prison system was gunned down in his Colorado home, and investigators are on a nonstop hunt for his killer.
"Tom Clements was someone who worked in a cold, dark world with a remarkably open and generous heart," said an emotional Gov. John Hickenlooper. He appointed Clements in 2011 to lead Colorado's prisons after Clements spent decades working to improve Missouri's corrections system.
Clements, 58, answered the door at his Monument home Tuesday night and was shot dead, the El Paso County Sheriff's Office said. Monument is about 50 miles south of Denver.
Hickenlooper seemed broken up about Clements' death as he spoke, and said he chose to go ahead with signing landmark gun control legislation the same day, as previously planned. The measures were pushed after 12 "Batman" moviegoers were shot to death last summer in Aurora, Colorado.
"And I think it's a coincidence, but an incredibly tragic and sad coincidence, that we have to process this all in a single day," the governor told CNN affiliate KUSA. But Hickenlooper said he was "all about carrying on."
Clements' wife, Lisa, urged the governor not to even think about delaying the signing.
"He would have expected us to sign these bills and go forward today," Hickenlooper said. "That's just the kind of man he was."
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. It becomes effective July 1.
Asked about a possible motive, Lt. Jeff Kramer of the sheriff's office 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.
"Because of the fact that Mr. Clements served in the position that he did ... we're sensitive to the fact that there could be any number of people who may have a motive for wanting to target him for a crime such as this.
"However, we also remain open-minded to all of the other possibilities as well because we don't want to follow one particular trail and find ourselves perhaps missing something along the way," Kramer said.
Reporters asked the governor whether Clements was "active" in his support for the new gun legislation, Hickenlooper replied: "He was supportive but he wasn't particularly active."
The lieutenant told CNN that Clements had not received any threats that authorities were aware of.
As news cameras trained on the governor while he signed each gun measure, investigators combed Clements' neighborhood, talking to neighbors and searching for clues.
One of those clues is a car that was seen near Clements' home at about the same time a 911 call was made by a relative in Clements' home telling authorities about the shooting.
A resident noticed a late-1990s model boxy vehicle, possibly a Lincoln, in the area, said Kramer of the sheriff's office. The resident told investigators that the car was about 200 yards from Clements' house on Colonial Park drive at about 8:30 p.m. and it was running but empty.
The 911 call was made at 8:37 p.m., Kramer said.
The resident told investigators that a few minutes after seeing the empty car, the resident saw the car again, but someone was inside and driving away. The car was headed in the direction of a road that leads to an interstate highway, Kramer told CNN.
Authorities said they are looking for a woman who may have information concerning that vehicle.
She was described as a white female, between 35-50 years of age. She was wearing light pants, a dark windbreaker and a hat, and may have been speed walking on Clements' street Tuesday night.
Officials stressed she is not a suspect, but is just someone they want to speak to.
They are not releasing the name of the relative who made the 911 call, but said the caller was the only other person home at the time.
Kramer added that it's unclear whether that relative was in the same room as Clements or in another part of the house.
Wednesday morning, Hickenlooper ordered flags in the state lowered to half-staff between sunrise and sunset until after Clements' funeral. Arrangements are still being made.
The governor repeatedly praised Clements Wednesday afternoon, calling him 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."
In addition to his wife, Clements leaves two daughters, Rachel and Sara, the governor's office said.
Clements' family released a statement through that office, thanking everyone for their support and concern.
"Our family has lost a devoted husband and a beloved father," it read.
"There are no words at this time to describe our grief and loss. We thank our friends and those praying for us here and across the nation. Your well-wishes and prayers bring us strength. We appreciate your continued respect for our privacy during this terrible loss."
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 reported from Colorado. Ashley Fantz wrote this story in Atlanta and Shawn Nottingham contributed.