(CNN) -- DNA has linked the slayings of three women, Philadelphia police said Tuesday night in announcing they are looking for a serial killer.
Authorities are offering a $30,000 reward for information leading to the arrest and conviction of those involved in recent homicides and assaults on women.
"We now know that this predator is responsible for three murders in this area," task force Capt. James Clark said at a news conference.
The reward offer comes as police and federal agents petition neighborhood residents for information in their joint investigation of the three killings and three other attacks on women in the Kensington area of Philadelphia.
The partially clothed body of the latest victim, Casey Mahoney, 27, was discovered December 15, according to police spokeswoman Jillian Russell. Mahoney had been sexually assaulted and strangled.
Police say Elaine Goldberg, 21, and Nicole Piacentini, 35, were killed in strangulation attacks in November.
Analysis showed the three were killed by the same assailant, Clark said.
Previously, DNA from the scene of the two earlier homicides was found to be from a single person, police spokesman Ray Evers said.
Authorities believe the attacker likely is still in the 10-block radius where the attacks occurred.
"We have detectives working day and night, following every tip," Clark said.
"It's time to bring this offender to justice," said Police Commissioner Charles H. Ramsey. "Help us stop this brutal violence from occurring in the future."
The location, the similar nature of the attacks and the descriptions of the attacker led police to suspect they are connected. The victims all were choked, police said.
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 white females involved in prostitution and narcotics, police said.