What to Know Safien Williams is accused in at least four rapes and sex assaults in South Philadelphia.

Williams has been employed by the city as an unskilled laborer.

Police are looking at Williams as a suspect in other sex assaults.

A city employee was charged Tuesday with sexually assaulting four women in South Philadelphia and investigators are working to determine whether he was involved in a string of additional assaults.

Philadelphia police arrested 37-year-old Safien Williams on Monday afternoon and searched his Earp Street home.

Williams was charged with two recent rapes on Mifflin and Bancroft streets, a recent indecent assault on S. 16th Street and a May 2018 rape on Morris Street. Police said in each case he followed the women during late night or early morning hours to their homes or places of business.

He asked one victim for a hug, another for a kiss, and then attacked them by striking the women over the head, police alleged.

Three of the incidents are tied to a recent string of assaults starting in December. Williams has not been charged in the other recent assaults, which all follow a similar pattern. But, investigators say they believe he has assaulted at least seven women and tried to assault two others. They don't currently have enough evidence to charge him with the additional assaults, police said.

Investigators also planned to go back and look into sex assault and rape cases occurring over the past two years, at least.

Philadelphia Police Commissioner Richard Ross called Williams a "very violent predator who essentially terrorized an entire neighborhood."

Police believe Williams is the man seen in recently released surveillance videos. After the release of the videos, investigators received numerous tips that Williams strikes a resemblance to the man caught on camera.

Investigators haven't released Williams' arrest photo as they continue to investigate him in the other cases, police said.

Police first put out an alert about a suspect in January. At that time, the attacker had allegedly assaulted three women in a 10-day period.

Investigators believe the suspect in the sex assaults used a bike and in almost every case, was armed with a knife.

On Monday, police recovered Williams' cellphone and some clothing they believe he used during the assaults. And, found a bicycle on a nearby abandoned property.

Williams has past criminal offense but no sexual offenses on his record, police said. It was unclear if Williams has an attorney who could comment on the rape charges he faces.

Williams was hired as a laborer with the city's Streets Department last summer, Ross said. There's no evidence Williams' employment status was related to the cases.

Investigators thanked the public for tips that have already come in. Ross urged more potential victims, no matter immigration status, come forward.

Anyone with more information is asked to call the PPD's Special Victims Unit at 215-685-3251/3252.