A second teenager is facing charges in last week's shooting at a Philadelphia charter high school for allegedly using a "guest" loophole to bring a gun into the school without triggering metal detectors.

Donte Walker, 18, is accused of supplying the gun that was used in the shooting inside the Delaware Valley Charter School Friday afternoon.

The shooting left a 17-year-old boy and an 18-year-old girl hurt.

Philadelphia Police Lt. John Stanford said surveillance footage from the school on the 5200 block of Old York Road in the Olney section of Philadelphia shows Walker entering the school shortly before the shooting as a "guest."

Walker, who graduated from the school last year, entered the building with a concealed black handgun and is seen handing over the gun to an unidentified man in exchange for cash in the gymnasium, according to Stanford.

Pictured at right is: Raisheem Rochwell (left) and Donte Walker.

The gun was then handed over to Raisheem Rochwell, Stanford said.

Walker faces charges including firearms violation and conspiracy.

According to Stanford, since Walker was a guest at the school he didn't need to go through a metal detector like students normally do.

"I would think it would be required for anyone coming into the school to go through the metal detectors. You have children's lives at stake here," Stanford said.

Investigators suspect Rochwell wanted the weapon because he feared he would be the target of an assault after school.

"If he's a target or not of a fight after school, that's still no excuse for him to have a firearm," Stanford said. "At the end of the day, you play with a loaded gun, things will happen."

Investigators have not confirmed whether they believe the 3:30 p.m. shooting was accidental, or if Rochwell intentionally fired the weapon. The female student was shot in the rear of her left arm. The bullet went through her bicep and then struck the male student in the shoulder, according to investigators.

Both victims were taken to Albert Einstein Medical Center. The girl was released on Friday while the boy was released on Sunday.

After a manhunt that included taking a 15-year-old boy into custody -- he was later released when police determined he wasn't involved -- police focused in on Rochwell and an unidentified 16-year-old boy. The 16-year-old turned himself in on Friday but was later released and not charged after questioning.

Rochwell turned himself in Saturday afternoon and remained behind bars Monday.

Rochwell's lawyer Amato Sanita said his client will be vindicated in the end.

Delaware Valley Charter School is one of 87 charter schools in Philadelphia. NBC10 reached out to Thomas Monson, the president of the school's Board of Trustees, for comment.

"We along with Philadelphia Police are investigating these events and will provide you with details as they become available," Monson said.

Philadelphia Police officers are not present in city charter schools because the schools don't fall under the Philadelphia School District's school police force. Security procedures are up to each individual charter school. That may change in light of the shooting, however, and how easily Walker was allegedly able to get inside the school.

NBC10 spoke briefly with Ernest Holiday, the school's CEO. Holiday said school officials are looking at surveillance video of the shooting and making security upgrades.

"We've been busy upgrading security to make sure that nothing like this happens again," he said.

He didn't go into specific details on what those upgrades will be however.

Late Monday afternoon, officials with the school sent a letter to parents.

"We have reviewed all security systems, processes, and procedures and heightened all of them to make certain our students and staff are safe," they wrote.

Officials with the school say they will have mental health personnel on hand when students return on Tuesday.