By Mike DeNardo and Jan Carabeo

PHILADELPHIA (CBS) — Police are trying to find out who shot four people outside a bar in Mount Airy overnight.

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Police say an argument inside the 7165 Bar on Germantown Avenue escalated to a fight that spilled outside around 2:30 a.m.

Police Chief Inspector Scott Small says a female bartender was trying to break up the fight when someone opened fire.

“The female employee was actually struck by gunfire. She was trying to help out and calm and stop the argument, when she got struck in the leg,” Small said.

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She’s in stable condition, as are two male patrons who were shot. But a fourth victim, in a car that crashed while speeding away from the shooting, is in critical condition.

Police were already in the area when they heard gunshots. They are now trying to sort out what happened and what sparked the argument that turned violent.

Investigators believe all of the victims and the shooter were inside the bar and restaurant before the gunfire broke out.

“We strongly believe the shooter was actually in the bar and restaurant,” Small said.

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Detectives are hoping surveillance video will help them identify the shooter.