The 15-year-old boy was brought in to police custody around 10:00 p.m.
One more teen will be arrested Friday and the others in the group, police say, were witnesses.
Detectives hit the streets Thursday night and were able to quickly identify all of the young men in the surveillance video they released earlier in the day.
The 15-year-old boy was charged with the beating of 64-year-old war veteran Edward Schaeffer.
Police say the teens, ranging from ages 14 to 17, were walking on North 5th Street in Olney Tuesday around 6:12 p.m. when the 15-year-old and another boy beat Schaeffer while the others stood and watched.
One of the teens in the video came forward to help authorities find the suspects that took part in the beating; tips also started coming in after Action News aired this video.
"We had a lot of help from juvenile probation, the school district police, a lot of citizens and a lot of phone calls and a lot of tips online," Lt. George McClay of the Philadelphia Police Department said.
Lt. McClay says they've made contact with all of the teens except one and he needs to come forward.
Investigators have also learned the motive for the attack was robbery.
"The complainant was on a cell phone as he walked by, so it was actually a robbery, what they did after that, no has been able to explain to me yet," McClay said.
Edward's wife Kate says she could barely recognize her husband when she saw him in a bed at Albert Einstein Medical Center.
"I never ever expected him to be as beat up as he was; my first impression was that someone took a baseball bat to his face and his head," Kate said.
Schaeffer lost his eye in the Vietnam War and he retired last year from a job where he helped disabled vets find work.
He and his wife want swift justice for the teenagers who apparently thought they had nothing better to do on a Tuesday night.
"This was just done out of nastiness. I have nothing to say to them or about them," Kate said.
Police have not released the names of the two suspects. At this point, they are facing minimum charges of robbery and aggravated assault.
Schaeffer's next door neighbor says she's sick about what happened. She says he's one of a kind.
"He's a good guy, I'm really, really sorry that happened to him," neighbor Michelle Harris said.
Schaeffer retired from the state labor department in May after spending 37 years helping disabled veterans find jobs.
Residents of the neighborhood were horrified to hear of the attack.
"People don't have hearts no more, they don't care and it's a shame. Where do you start caring about your other human beings? Come on. You got the fellow man to care about. It's just a shame. It really is," Olney resident Marion McCloud said.
Schaeffer will undergo surgery tomorrow for his facial and skull injuries.
