"We have a volatile situation, an unsettling situation, it's dangerous. We have male with a gun approaching these young girls on the highway," Captain John Darby of the Philadelphia Police Special Victims Unit said during an afternoon press conference on Monday.
The suspect is described as a black male in his late 20s to 30s, about 5'7 to 5'9 tall, with a light complexion, and a medium to stocky build.
In most of the incidents the suspect was wearing dark colored clothing. However, he was wearing a white t-shirt and blue jeans in the latest alleged assault.
Police say he conceals his face by pulling over a hooded sweatshirt or wearing a mask.
In one incident, the suspect used a dark colored mountain bike to flee the scene.
"What it shows is the clear intent of this male. In none of these cases was there a demand for money; we believe sexual assault was the motivator," Darby said.
All the victims were between 12 and 17 years old.
"We have identified a possible pattern," Darby said prior to reading the timeline of the four sex assault incidents.
The first reported incident took place around 7:30 a.m. on Tuesday, March 19th. The suspect approached a 12-year-old girl waiting for a school bus on the 11000 block of East Price Street. Police say he directed the girl point of gun to an alley where he assaulted her.
On Tuesday, April 23rd around 11:00 p.m. a 17-year-old was walking on the 900 block of East Chelten Avenue when she was approached by a man. He produced a gun and forced her behind a commercial property.
Police released surveillance of the next reported incident which took place on Sunday, May 19th. About 10:45 p.m. the suspect was riding a mountain bike and passed a 15-year-old girl who was walking along the 600 block of East Wister Street. Moments later, he dropped the bike and returned to the girl. He pulled out a gun and took her into an alley where she was sexually assaulted.
The most recent incident took place 12:30 a.m. Sunday on the 1100 block of East Chelten Avenue. A man with a gun approached a 17-year-old girl and directed her to follow him to a vehicle. At the entrance to the Lonnie Young Recreation Park, he pushed the girl inside and assaulted her at the entrance gate.
Darby said they are looking at any incident with a gun in the area to see if they are connected.
Anyone with information is asked to contact police.