Yes, many prisoners who have committed serious offenses can reform themselves. If the justice system is able to fulfill their duty of rehabilitating citizens, it will be the case that many offenders can reform. However, this is only possible if the objective of incarceration is rehabilitation and not purely punishment.
Anybody can change if they have made a decision to do so. We all have a free will and a choice that enables us to make decisions in life, good or bad. Prisoners with serious offenses and have shown transformation should be released but on recommendation from the correction facilities officers.
Yes, I believe any prisoner with any offense, no matter how serious has the potential to reform. It is completely based on the individual circumstances though. How much does the offender want to reform. Does he want to reform for the right reasons? Some people have to hit rock bottom before they realize it is time to begin anew.
Our personalities are formed very young. By age five, a person is who they are going to be. Most of the time a person who ends up in prison has had a very rough childhood. By the time they are in prison, there is so little that society can do to help anyone truly reform.