The Hridaya Vihara Sangha began in 1996 with a group of 5 prison inmates from different backgrounds (Vietnamese, Cambodian, American, Latin American, and African American) all serving different prison terms. First they made an official request for Buddhist clergy. Then they made an appeal to the nearest Buddhist temple asking for help with their spiritual needs.
A response came from the International Buddhist Meditation Center in Los Angeles when Rev. Kusala agreed to help. After several months, he passed the position on to fellow priest, Rev. Kshanti who began visiting the prison at least 3 days a week on a volunteer basis for the next 4 years.
In the meantime, the group of 5 grew to over 100 prison members! This is in addition to a handful of Dharma teachers and lay volunteers that give their time on holidays and special occasions.
Most of the inmate members are still at LAC-CSP Lancaster. Some have paroled and others have transferred to other prisons. Also, some of them have release dates, and some don't.
For more about Buddhism in Prison, see writings and publications.