Philadelphia Police said at a news conference on Thursday morning that an 18-year-old has been arrested. However, they are not yet releasing a name since he remains the subject of other criminal investigations.
Police say it was around 10:00 p.m. on Tuesday night at 48th Street near Springfield Avenue when a boyfriend and girlfriend were headed home after dinner at a restaurant.
That's when they were approached by two teenagers, one described as about 13 years old while the other was the 18-year-old.
With guns pulled, the teens announced a robbery.
"Once you have a gun, you have all the power," the boyfriend told Action News Wednesday night. "I was cool the whole time and kept looking at his gun."
"I was trying to make a decision if I was going to go for the gun, but she was pleading for me not to, that she needed me here."
The man, who does not want to be identified, says they didn't have enough cash, so the older teen angrily grabbed the two, pulled them into an alley and raped the woman.
The boyfriend says he was forced to watch the teen sexually assault his girlfriend at gunpoint.
Police say the 13-year-old begged his friend to stop and ran away before the attack.
"I could tell he really didn't want to be a part of it," the boyfriend said. He added that his girlfriend is recovering and he revealed to Action News she's a school teacher.
"Which makes it even more difficult for her to go back to work. I mean it really is a life changing event," the boyfriend said.
The victim's purse and some other belongings were found just a block away in a recycling bin.
Police say the quick arrest 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.
A search for the 13-year-old continues.
The police say the 18-year-old suspect may have been involved in numerous other crimes, but, they believe this is the first involving sexual assault.