Investigators say they're closer to solving the mystery of who murdered a federal prosecutor more than 16 years ago, but they need the public's help. The reward for information in the case has been raised from up to $1 million to more than $1.5 million after previous leads went nowhwere, reports CBS News correspondent Tony Dokoupil.

Tom Wales

On a chilly October night in 2001, Assistant U.S. Attorney Tom Wales was at home, sitting in his basement office, when a gunman shot multiple rounds through the window. Wales was an 18-year veteran of the U.S. attorney's office in Seattle.

"The killer was familiar with Tom's property and his work habits," former Seattle U.S. Attorney Michael McKay said.

The shooter was careful to avoid setting off flood lights attached to the yard's motion detectors, leading investigators to believe it was a carefully planned execution. More than 16 years later, the killer is still at large, and the case was recently the subject of a five-part podcast, "Somebody Somewhere."

"They say it was the perfect murder. But I'm not buying it," the podcast says.

Investigators aren't buying it either. They came together Wednesday in a Seattle conference room named after the fallen U.S. attorney, asking for the public's help to solve the case.

"We have a lot of investigative theories right now. We have several that we're very fond of, and we need more information," FBI special agent Jay Tabb said.

"I think they have people identified that they think are the perpetrators," said John McKay, former U.S. attorney for the western district of Washington. McKay took over as the U.S. attorney in Seattle shortly after Wales was killed.

"They're waiting for someone in their circles to come forward and give them maybe the last couple of pieces that will push them over the finish line," McKay said.

Early on, investigators identified a suspect, a commercial airline pilot, who denied any involvement and was never charged. Through bullet casings, they say they identified the weapon but they apparently never found it. Wales' daughter suggests her father's duties as a prosecutor might have played a role in his murder.

"If a federal prosecutor can be brutally murdered for carrying out his prosecutorial duties, the law enforcement and judicial processes that keep all of us safe are fundamentally compromised," Amy Wales said.

If Wales was targeted because of his job, he would be the first and only U.S. attorney killed in the line of duty. In an indication of how committed Wales' former colleagues are to solving the case, they're among those who opened their wallets to increase the reward for information.