Law students at the University of Denver sued the federal Bureau of Prisons today on behalf of a man kept in solitary confinement for 24 years.

The lawsuit, filed in Denver federal court, said the incarceration of Thomas Silverstein amounts to cruel and unusual punishment.

Silverstein, 55, is being held in total isolation at the Supermax prison in Florence.

He has been in prison since 1975 and in solitary confinement since the 1983 murder of a prison guard at the federal prison in Marion, Il. He previously was convicted of killing two inmates at prisons in Marion and Leavenworth, Kan., in 1981 and 1982. His conviction for killing a third inmate was overturned and never retried.

Silverstein was put on permanent "no human contact" status after the 1983 murder of the prison guard. His isolation for 24 years has led to deterioration of his mental health, the lawsuit said.

The conditions of his confinement caused him to "suffer deprivations that cause mental harm that goes beyond the boundaries of what most human beings can psychologically tolerate," the lawsuit charged.

Kept in soundproof cells, he has been subjected to extreme heat and constant bright lights in his cells, the lawsuit said. His only visitors were strangers who volunteer to visit prisoners or persons he knew before he was incarcerated.

Silverstein developed an interest in Buddhism and other religions which he has not been able to pursue, the lawsuit charges. It took years for him to be able to listen to the radio, play tapes for his studies or have access to art supplies, the lawsuit said.

Silverstein has demonstrated for 15 years that he no longer poses a threat to staff or inmates, the lawsuit said. Her has not violated a prison policy or received a misconduct citation for more than 20 years, the lawsuit said.

He exhibited nonviolent behavior even when inmates released him during a prison riot in Atlanta in 1987, the lawsuit said.

He was moved to Supermax in 2005 believing he would be able to demonstrate his ability to function in the general population. Although he complied with prison requirements, officials have refused to consider reducing the level of his confinement, the suit said.

At Supermax, he is confined in a sound-proof room with 24-hour camera surveillance. His art supplies have been taken away.

He is being held in total isolation while other inmates who have murdered guards or inmates while in prison are not, the lawsuit said.

As a result of his isolation, Silverstein has suffered depression, hallucinations, memory loss and other mental and physical harm, and is in danger of succumbing to mental illness, the lawsuit said.

The suit seeks a court order to remove him from solitary confinement and place him into the general population, to give him access to religious materials and to relax restrictions on his communication with visitors and attorneys.

DU law students Steven Baum and Amber Trzinski filed the case under the supervision of visiting professor Dan Manville, a prisoner's rights expert, and associate professor Laura Rovner, as part of the school's Civil Rights Clinic.

Earlier this year, Rovner led a team of student lawyers in a case that overturned a Bureau of Prison rule barring inmates form publishing articles and stories under their own name.

The Civil Rights Clinic is a year-long class in which students do all the work, preparing the lawsuit, following up on motions and arguing in court under a federal provision for student lawyers.