Head of Colorado's prison system, Tom Clements, shot to death in his Monument home Tuesday night

MONUMENT, Colo. -- The head of Colorado's prison system was shot to death in his Monument home Tuesday night, and authorities say the shooter is still on the loose.

Tom Clements was shot at about 8:30 p.m. when he answered the door at his house in the 17400 block of Colonial Park Drive, according to El Paso County Sheriff's Lt. Jeff Kramer.

Kramer says a family member called 911 to report the shooting.  No one else in the home was hurt.

Investigators do not have a description of the shooter, but began searching the area Tuesday night.

"We did have some efforts from our K-9 unit to see if they could locate anything that might be helpful in this investigation, those efforts have been met with negative results," said Kramer.

Authorities were going house to house Wednesday morning trying to find out what neighbors knew about the shooting, Kramer said.

Governor John Hickenlooper announced flags will be at half-staff at all public buildings statewide, until the day after Clements' funeral. Those arrangements are pending.

Hickenlooper released an email at 3:30 a.m. Wednesday that said he “can hardly believe it, let alone write words to describe it.”

Hickenlooper will be holding a press conference at the capitol around 8 a.m., said Colorado Department spokeswoman Alison Morgan.

“We are sad, we are very sad," Morgan said.

Clements was appointed as the Executive Director of the Department of Corrections in 2011.

He is survived by his wife, Lisa Clements, and his two daughters.