Phoenix police on Saturday said they believe a series of 13 random shootings since May may be connected.
If that's true, it would make the third ongoing investigation into violent serial criminals detectives in Pheonix are trying to solve simultaneously.
A task force of detectives already is trying to track down a serial killer dubbed the Baseline Rapist who they believe is responsible for five killings and a series of rapes and assaults that began last August.
They're also investigating a series of at least 25 random shootings of animals - three horses and five dogs, according to The Arizona Republic - and people that has left several people dead since last May. They believe they're related, but don't have proof that all are connected.
"The only thing that ties the three series together is the victims all appear to be random," Phoenix police Sgt. Andy Hill told The Arizona Republic on Sunday. "I have not seen anything like this in my 22 years."
Saturday, Sgt. Andy Hill said it appears a third series of shootings that began May 2 could be the work of another suspect or suspects.
Thirteen shootings are believed to be connected, none fatal, including two early Saturday, twenty minutes apart, that left a man and a woman wounded.
One happened at about 2:40 a.m. Saturday near 44th Street and East Devonshire Avenue, where a woman was shot in the head as she was walking. About 20 minutes later a man out walking on Van Buren Street east of 48th Street was shot in the back.
The most recent shootings follow 11 others that began on May 2, Hill said. Detectives are not positive all are linked but evidence and circumstances lead them to believe they are.
The incidents happened late in the evening or early in the morning, and most involved people walking or riding bicycles. Most happened along Camelback Road, Indian School Road, Van Buren Street or in the 44th Street area. Police believe the individual or individuals drive a vehicle, possibly a sedan, The Arizona Republic reported.
"This person or persons is out there, driving around, and they are looking for somebody," Hill told The Arizona Republic.
This has some Phoenix residents concerned. Security worker Thomas Young, 46, told the newspaper the idea of a third series of related crimes makes him feel "very uncomfortable" since he often walks about an hour and a half home from work early in the morning on weekends, when buses don't run.
There's nothing to link the recent cases to the earlier serial crimes, Hill said.
Hill urged the public to be cautious and extra aware of their surroundings.
He asked anyone with information on the recent shootings or the other serial crimes to call the Silent Witness line at 602-261-8600.
© 2006 CBS Interactive Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.