Tom Clements, the head of the Colorado Department of Corrections, was shot as he answered the door and authorities say there still isn't a sign of a suspect or a motive. NBC's Kristen Dahlgren reports.

Authorities are asking the public for help finding an unknown gunman who shot dead the executive director of Colorado’s department of corrections at his home Tuesday night.

Police believe the director, Tom Clements, was shot when he answered the door of his Monument, Colo. home. Why and by whom remain a mystery.

"Because of the fact that Mr. Clements served in the the position that he did as the executive director of the Colorado Department of Corrections, we're sensitive to the fact that there could be any number of people who could have a motive for wanting to target him," El Paso County Sheriff's Department spokesman Lt. Jeff Kramer said at a press conference Wednesday afternoon.

There was one other person in the house at the time of the shooting, who was not injured, according to police.

The El Paso County sheriff's office is now turning to the public for any information from those who may have been in the area at the time of the shooting or may have seen the car the suspect is believe to have used to flee the scene.

A Colorado law enforcement spokesperson says police are appealing to the public for more information on a car seen near the house where Dept. of Corrections chief Tom Clements was shot.

The sheriff's department announced they are currently searching for a white female between the ages of 35 and 50 who may have been speed walking in the neighborhood at the time of the shooting. The woman is not a person of interest, but may have made "some observations that could be valuable to us," Kramer said.

Police have a vague description of a vehicle that may be connected with the shooting. Kramer said a witness saw a dark colored boxy, two-door car that was unoccupied and in the area of the shooting around 8:30 p.m local time. The car was left running at an intersection about 200 yards away, according to authorities.

The vehicle was seen again after the shooting with one occupant but no description of that person.

The wooded area where the shooting took place is largely rural, but Kramer said police will also be checking surveillance video of nearby shopping centers to see if they can find a license plate number or any additional helpful information.

The governor addressed Clements' shooting in a letter sent to all Department of Corrections employees early on Wednesday, Hickenlooper spokesman Eric Brown told NBC News in an email.

“Last night, Tom Clements was killed at his home in Monument,” Hickenlooper wrote in the message. “I can hardly believe it, let alone write words to describe it.”

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Hickenlooper praised Clements as a man who was “unfailingly kind and thoughtful.” The governor ordered all flags lowered to half-staff in the state on Wednesday.

“He was a great friend to me and I think all of us. In many ways he helped define who a public servant is,” said Hickenlooper, who appeared to hold back tears at a press conference. “He is going to be deeply, deeply missed.”

News of Clements' death came as Hickenlooper was expected on Wednesday to sign new gun bills limiting ammunition magazine capacity and expanding background checks on firearm purchases in the state, eight months after the Aurora movie theater shooting.

Whether or not Clements’ position as director of the Department of Corrections played a role in his death remains under investigation.

Colorado Department of Corrections via Reuters Tom Clements, the executive director of the Colorado Department of Corrections

“We’re sensitive to the fact that serving in that type of position could in fact make him a target of folks that would have motive to target him for a crime such as this,” Kramer said at a press conference Wednesday morning. “However we’re making sure that we remain open-minded to a number of other theories as well.”

One such theory is that the shooting could be connected with a 2006 case in Colorado involving Homaidan al-Turki, who was convicted of repeatedly raping an Indonesian maid that he kept as a virtual slave in his basement in Aurora for four years.

Last week, Clements turned down the transfer of Al-Turki back to Saudi Arabia.

Kramer acknowledged authorities are aware of the information and were taking it into consideration. "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," he said.

A federal official told NBC News that no federal agents have been involved in the investigation. The FBI offered assistance but so far state authorities have declined the help, saying they have the resources they need.

Clements wrote about the challenges faced by corrections officers in a message posted on the Departments of Corrections website – including the violent death of one officer in September.

“Together we are ‘building a safer Colorado for today and tomorrow,’” Clements wrote in the message.

“He was an inspirational leader,” Alison Morgan, a spokesperson for the Department of Corrections, said on Wednesday. “He had a vision for the department and was exceptional at sharing that vision with staff and inspiring the 6,000 employees of the department.”

He is survived by his wife, Lisa, and daughters Rachel and Sara.

Clements was confirmed as the head of the state’s department of corrections in February 2011 in a unanimous vote of the state senate. He had previously worked as director of operations for adult correctional facilities in Missouri, and had over three decades of experience working in corrections, according to a 2011 press release from Hickenlooper’s office.

The Department of Corrections had a budget of $737 million in 2012, and monitored a total inmate population of more than 20,000.

NBC's Pete Williams contributed to this report

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