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PHILADELPHIA (CBS) — Police provided new information on the West Philadelphia triple shooting on Friday that left 17-year-old Sandrea Williams dead and two teenage boys hospitalized. Philadelphia police believe the shooting was related to petty neighborhood disputes among kids and that the two gunmen are teens themselves.

“It’s a miracle there weren’t anymore casualties,” said Philadelphia Police Capt. Jack Ryan.

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According to Ryan, there were at least 6 kids present at the time of the shooting.

About 23 shots were fired in seven seconds.

Authorities say Sandrea’s mother was sitting on the front steps and witnessed the tragedy unfold.

“I heard someone scream Sandrea, Sandrea, Sandrea three times,” a neighbor told Eyewitness News.

Sandrea was gunned down just after walking away from her steps where she was sitting with her mother.

“Her mom just looked so blank in the face like she was in pure shock,” another neighbor added.

Investigators say just before 11 p.m., the two gunmen fired into a group of kids, striking two teenage boys and killing Williams on the 300 block of North Simpson Street.

Philadelphia Police Lt. John Walker says the gunmen shot Williams in the neck, leg, and back as she was standing in the driveway with her 17-year-old friend, who is in stable condition at Penn Presbyterian Medical Center.

Credit: CBS.

Investigators add that a 15-year-old boy, who was standing on the same street at the time, was also shot and is in stable condition at Lankenau Medical Center.

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It’s unclear whether he knew the two other teenagers.

Police say the gunmen were on foot, not car when the ambush occurred.

Right now, investigators are still looking for the two gunmen.

A $20,000 reward is being offered for information leading to an arrest or conviction.

If you have any information, call police at 215-686-TIPS or 215-686-3334.