JOIN USThe prisoners were waiting outside a courtroom when the gunmen fired at them, killing three men instantly, while another man succumbed to his injuries later, police officials said.
One of the gunmen was captured while three others escaped.
Police launched a search operation to trace them.
Police officials linked the attack to a rivalry between two criminal gangs that are active in Rawalpindi.
Chaudhry Shaukat, the leader of one gang, and his brother were among those killed this morning.
Several members of both gangs have been killed in attacks in the past, police said.
Media reports said the gunmen had hidden their weapons under shawls.
The gunmen were not searched when they entered the court complex.
There have been several instances of attacks in court complexes in both Islamabad and Rawalpindi involving members of rival groups over the past few years.