I can't believe it would be possible to charge him with murder, but maybe some other charge or even a civil suit.
The suspect was arrested in 1966 and charged with aggravated assault. He was convicted and sentenced to 15 years in prison. He has since been released. He was arrested by the Philadelphia Police Department after Patrolman Barclay died, however the District Attorney has yet to make a decision on formal charges.
http://www.policeone.com/news/1343397/