Mayor Nutter hopes an aggressive use of cash rewards will prompt more community cooperation with preventing crimes - possibly enough to help stem a homicide rate that has flared to a troubling level this month.

From now on, the city will offer $500 for information leading police to an illegal gun and up to $20,000 for information leading to an arrest in any homicide.

"To every criminal out there: I just put a $20,000 bounty on your head," Nutter said at a news conference Thursday at Strawberry Mansion High School in North Philadelphia. "We are coming for you. We will find you. People will give up that information."

Nutter also announced that the city would double the funding provided to the witness assistance program of the District Attorney's Office.

When asked about this week's killing of Kensington store clerk Rosemary Fernandez-Rivera, a potential witness in a murder case who was shot by a gunman after being interviewed by detectives, Nutter said communities as a whole must stand up against criminals.

"We have to decide, as citizens . . . we're not going to be held hostage by these domestic terrorists in our city any longer," he said.

Nutter said he included money for more rewards for crime tips in this year's budget. He also has authorized Police Commissioner Charles H. Ramsey to immediately assign more officers to crime hot spots by using overtime funds.

Reinforcements are on the way. A class of 120 newly minted officers will start hitting the streets in March, and up to 100 additional officers will join the Police Academy in June.

Privately, however, members of the department said the 6,500-person department's staffing levels were so low that several more rounds of hires were needed to make an impact.

In 2006, the murder tally in Philadelphia climbed to 406, the highest in more than a decade. That year, 29 people had been killed by the end of January. The 2012 homicide tally stands at 31 as of Thursday evening.

Several high-ranking police officers, who asked not to be named, said many of the murders committed this month defied typical patterns. Kevin Kless, a recent Temple University graduate, was beaten to death Jan. 14 in Old City after a random argument. Two teenagers were fatally shot Jan. 10 in Juniata Park by a man who opened fire into their car after a neighborhood dispute. Earlier that day, a man and a woman were stabbed to death inside a South Philadelphia apartment. Wednesday, police found two dead at the scene of a murder-suicide in a house in Logan.

"Some of the incidents would be impossible to prevent," one veteran officer said. "There are some cases that are just bizarre, and those you can't predict."

Nutter and District Attorney Seth Williams said they would push for stronger sentences for those arrested on weapons charges. Nutter said he wanted gun crimes to result in prison time in every case, as allowable by law.

"Got a gun? Go to jail," Nutter said. "No more slaps on the wrist. No more falling through the cracks. No more walk away and think that nothing else is going to happen to you."

Williams said the city was "throwing everything and the kitchen sink at this problem."

The city also will develop a "gunstat" program that will track guns used in crimes and track offenders, including those on probation and parole.

"We will be zeroing in on the causes of gun violence," Nutter said. "Our goal is to develop information so that we can set priorities and direct our resources to where they are needed."