Police had already arrested an 18-year-old male suspect Thursday.
Police say it was around 10:00 p.m. on Tuesday night at 48th Street and Springfield Avenue when a boyfriend and girlfriend were headed home after dinner at a restaurant.
That's when they were approached by two teenagers, the 18-year-old man and 18-year-old woman.
With guns pulled, the teens announced a robbery.
The boyfriend says they didn't have enough cash, so male teen angrily grabbed the two, pulled them into an alley and raped the woman.
The boyfriend says he was forced to watch at gunpoint.
He says the 18-year-old woman ran off before the sexaul assault.
The victim's purse and some other belongings were found just a block away in a recycling bin.
Police say the quick arrests should serve as a warning to others.
"If you're going to perpetrate these crimes, I think the message is you'd better look over your shoulder," said Capt. John Darby of the Philadelphia Police.
The police say the 18-year-old male suspect may have been involved in numerous other crimes, but, they believe this is the first involving sexual assault.
Earlier reports believed the 18-year-old male was with a 13-year-old male, but this turned out not to be the case.