PHILADELPHIA (CBS) — One suspect is in custody, and police are looking for others, following three attacks just steps away from SEPTA stations.

The robbery spree happened over a span of a month and within a few blocks in South Philadelphia.

Police say the group watches their victim, sometimes as that person leaves the subway, walk with them for a block and then attack.

“They came up behind a person and assaulted them, knocked them to the ground, kicked them and stole some money,” said Capt. Frank Milillo.

Police in the Third District are investigating three separate, though similar, incidents.

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The first attack was a violent beating on the 1200 block of South Broad Street, near the Ellsworth Federal Station, on Jan. 10.

“As far as my knowledge goes, nobody has submitted any tips that they have identified these offenders at this date,” said Milillo.

There has been an arrest in two other crimes, similar M.O., with the first arrest coming Feb. 6.

Teens were seen posing for the camera leaving the Tasker-Morris Street Station. Afterwards, a 22-year-old man was attacked and had his phone stolen.

Two days later, two blocks away on Pierce Street, there was another robbery where the victim’s phone was stolen.

“We ping his phone that was taken, leads us to 1600 Westmoreland area,” said Milillo.

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That’s where a 15-year-old teen was arrested and was charged for two of the three robberies. Police are still looking for other teens involved.

“It’s still an active investigation. They’re still looking into his accomplices and South detectives are still looking into it,” said Milillo.

While police work the case, those living in the area are taking extra precaution.

“I look around to see what’s going on to see if there is a group in front of me, group behind me, group beside me. Yeah, I’m aware of that,” said Billy Dunbar.

“I don’t carry a handbag at all for fear that somebody will hit me over the head,” one woman said.

Police say there are at least three other teens involved in the attacks. Authorities are asking the public to call them with any information.