The car was a Citroen C3 that had been reported stolen, the Italian news agency ANSA reported.
Domenico Cutri, 32, was being transported to a court hearing Monday when the prison van was attacked outside Milan by armed men, police said. The gunmen succeeded in freeing him after a shootout, but a short time later his mother took his mortally wounded brother, Antonino, 30, to a hospital.
Cutri is serving a life sentence for killing Luckasz Kobrzeniecki in 2006. Prosecutors said Cutri arranged the killing because Kobrzeniecki was bothering his girlfriend and Cutri drove the car from which another man fired at the victim.
Cutri had not been found Tuesday.