LOS ANGELES  - Police in Colorado were hunting a gunman who shot dead the US state's prisons chief, even as its governor signed new gun laws into force following the Aurora theater massacre. Tom Clements, head of the Colorado Department of Corrections, was shot in the chest at point blank range, when he answered the front door at his home in Monument, 50 miles south of Denver, police said. Gov John Hickenlooper fought back tears at a news conference saying Clements "dedicated his life to public service," according to the Denver Post. He was speaking as he signed three new laws into force, notably requiring background checks for private and online gun sales and ban ammunition magazines that hold more than 15 rounds. "When we as a community tried to process the shootings that took place last July in a dark movie theater, we spent a great deal of time ... trying to look at what could we as a state do," he said, referring to the Aurora massacre. "Large magazines have the potential to turn killers into killing machines," said Hickenlooper. The Aurora shooting, in which disturbed student James Holmes allegedly opened fire at a midnight screening of the Batman movie, "The Dark Knight Rises," killing 12 people, revived America's perennial gun control debate.