More than 2,000 anonymous tips have been called in to Phoenix police as they try to capture two serial killers who have terrorized parts of the city.

The "Baseline Killer" has been raping, robbing and killing since last August, resulting in six deaths.

The "Serial Shooter" is believed to be responsible for 34 random shootings since May 2005. Five people are dead, and 16 were wounded, according to authorities.

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Both killers choose their victims randomly and are thought to lurk in the area before they attack.

But police say a composite sketch of the Baseline Killer likely is a disguise, and the Serial Shooter hasn't been seen.

"Because of the circumstances right now, it's going to take a tip," said Sgt. Paul Penzone, who oversees the Silent Witness program. "It may take some luck, and it's going to take hard work by investigators to solve these crimes.

"It's critical that everyone take an attitude that they won't tolerate it, and they're going to partner with the Police Department to put it to an end," Penzone added. "This is our job, but it's everybody's responsibility to make a difference."

Officials said that just about every call coming in to Silent Witness this week has been about the serial killers.

Callers remain anonymous and all tips are prioritized, partly based on the details provided and the urgency of the information.

"Sometimes, the smallest tip makes the difference," Penzone said.

While more than 100 Phoenix police officers search for the serial killers, authorities have been telling residents to report any person or activity that looks suspicious in their neighborhoods.

Six phone lines are ringing non-stop with so many calls that tipsters sometimes get a busy signal or find themselves momentarily put on hold.

"There's an old saying in police work that 90 percent of good police work is luck. It's being in the right place at the right time," said police Detective Mark Potts, who has been working 18-hour shifts answering phones. "This could be the tip that puts us in the right place. This is where it's going to happen. It's either going to be that or luck."