Twenty-three-year-old David Smith is being held on a dozen charges, including rape, sexual assault, and multiple firearms charges.
Police picked him up Wednesday night as a person of interest.
Smith has a preliminary hearing scheduled for July 18.
Police tell Action News they believe that the person of interest being questioned in the sex assault of a teenager is the man who committed the crime.
Police say the man arrested, is a 23-year-old from Philadelphia who was carrying a gun illegally.
He was taken into custody just before 6 p.m. in Upper Darby after SEPTA police stopped a person resembling the suspect description.
Officers said he was in possession of a loaded Glock 9mm handgun.
Shortly before 6pm, a recent graduate of the Police Academy, Transit PO Baron and his FTO, PO Clark stopped a person resembling the rape suspect. He was in possession of a loaded Glock 9mm. @PhillyPolice SVU has pounced on this possibility. KEEP THE TIPS COMING! pic.twitter.com/IJHoCMYg2h— Thomas J. Nestel III (@TNestel3) July 5, 2018
"We strongly believe, based on what we have, that he is the person. So I just wanted to give some assurances that we believe it's him. That said, Special Victims still has a lot of work to do, firmly connecting him to the crime and making sure we have everything firmed up for a successful prosecution," said Capt. Sekou Kinnebrew.
The attack happened during one of the busiest days of the year -- the time when many people were going to holiday festivities.
Authorities say the man walked up behind the 17-year-old victim just before 10 p.m., pulled out a gun, forced himself on her and performed a sex act.
"It appears he's armed with a gun and he confronts her with that gun then attacks her," said SEPTA Police Chief Thomas Nestel.
The suspect then fled the scene.
Police responded to the scene shortly after the attack after receiving a call from the victim.
"This is an unusual event for us. This is horrifying," Nestel said. "What he did was vile."
Veronica Ilg of West Philadelphia said, "To see that type of behavior is just discouraging and unsafe and in the city of Brotherly Love. I mean how ironic is that I am very happy he was captured."
Monica Garcia of Northeast Philadelphia added, "I always catch the SEPTA with my kids all the time and it is really scary. Thank God they actually caught him."
The Philadelphia Police Department Special Victim's Unit is leading the investigation, with support from SEPTA Police Department investigators.
Police say the victim didn't know her attacker and no other passengers were near the incident.
Send a News Tip to Action News
Learn More About 6abc Apps