(CNN) -- An unofficial watch group is forming in a central Philadelphia, Pennsylvania, neighborhood, residents say, in an effort to protect themselves against a serial strangler responsible for at least three homicides.
The 12-member unit has been patrolling the city's rough-and-tumble Kensington district since Friday, two days after the partially clothed body of the latest victim, Casey Mahoney, was discovered.
"We are warning residents to go out in pairs," said group organizer Tom Potts. "I've been talking to women in the area. Most are carrying pepper spray." One of women has been walking with an electric stun gun, he added.
Police are also trying to determine whether three strangulation assaults that occurred in the same area are also linked to the suspected killer.
The victims were all white females, police said.
Potts said the neighborhood group walks up and down Kensington Avenue and nearby streets each night in the drugs- and prostitution-riddled neighborhood.
Their actions come as police ask residents for information of those involved in the attacks, but also warn the public against taking matters into their own hands.
"We are cautioning people to wait and get the person identified," said police spokesman Ray Evers. "We need the public to be our eyes," he said, warning against the potential dangers of vigilante action.
Some residents are pairing up when walking at night.
"I've never felt safe alone," said Arianna Hall-Reinhard. The 22-year-old Kensington resident says she carries pepper spray and joins friends when she heads home from work. "It's a whole new level of having to be aware," she said.
Others have taken to social media, joining a Facebook page called "Catch the Kensington Strangler, before he catches someone you love."
The page featured an incorrect sketch of the suspected killer, prompting police to contact the site, Evers said.
Elaine Goldberg, 21, and Nicole Piacentini, 35, were both killed in November attacks.
Mahoney had been sexually assaulted and strangled on December 15, said police spokeswoman Jillian Russell.
DNA has linked the slayings of three women, and authorities are offering a $30,000 reward for information leading to arrests and convictions, said task force Capt. James Clark.
"We now know that this predator is responsible for three murders in this area," he said.
Authorities say they believe the attacker likely is still in the 10-block radius where the attacks occurred.
"It's time to bring this offender to justice," Police Commissioner Charles H. Ramsey told reporters. "Help us stop this brutal violence from occurring in the future."
But authorities say they lack corroborating DNA evidence linking the assaults to the homicides because too much time had elapsed between the initial two assaults in October and when the victims notified police.
"The assault victims did not come forward until police began combing the Kensington (neighborhood) for suspects and potential victims following the November homicides," Evers said.
Federal agents joined the investigation earlier this month, bringing in resources from the FBI's behavioral analysis unit, violent criminal apprehension program, and National Center for the Analysis of Violent Crime.
"The investigation appears to be limited to Philadelphia," said FBI spokesman J.J. Klaver. "This could change if there are any indications that the subject or subjects responsible for the crimes ... are linked to similar crimes elsewhere."
The assault victims described the attacker as an African-American male in his early 20s, weighing between 160 and 170 pounds.
Police said a third assault victim was pulled into an alley earlier this month. Despite being choked, punched and hit on the head with a brick, the 33-year-old woman escaped, and her assailant fled the scene, according to a police report.
All victims were involved in prostitution and narcotics, police said.