Inmates serving a jail sentence make a phone call at Maricopa County's Tent City jail in Phoenix July 30, 2010. (Photo by Joshua Lott/Reuters)

Cori Walters, 32, (R) hugs her daughter Hannah Walters, 6, at California Institute for Women state prison in Chino, California May 5, 2012. (Photo by Lucy Nicholson/Reuters)

Marvin Caldwell, 63, who said he was imprisoned for 20 years under the three strikes law for possession and sale of methamphetamine, looks out of his cell at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Jail cells are seen in the Enhanced Supervision Housing Unit at the Rikers Island Correctional facility in New York March 12, 2015. (Photo by Brendan McDermid/Reuters)

Chris Willis, 34, works out in the exercise yard at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Administrative segregation prisoners take part in a group therapy session at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Inmates walk around a gymnasium where they are housed due to overcrowding at the California Institution for Men state prison in Chino, California, June 3, 2011. (Photo by Lucy Nicholson/Reuters)

Inmates stand in a gymnasium where they are housed due to overcrowding at the California Institution for Men state prison in Chino, California, June 3, 2011. (Photo by Lucy Nicholson/Reuters)

Inmates exercise at the California Institution for Men state prison in Chino, California, June 3, 2011. (Photo by Lucy Nicholson/Reuters)

Corrections officers work in the Enhanced Supervision Housing Unit at the Rikers Island Correctional facility in New York March 12, 2015. (Photo by Brendan McDermid/Reuters)

A jail cell is seen in the Enhanced Supervision Housing Unit at the Rikers Island Correctional facility in New York March 12, 2015. (Photo by Brendan McDermid/Reuters)

Women chat as they lie in beds placed in the communal area outside cells, due to overcrowding at the Los Angeles County Women's jail in Lynwood, California April 26, 2013. (Photo by Lucy Nicholson/Reuters)

An inmate looks out from his cell in the Security Housing Unit (SHU) at Corcoran State Prison in Corcoran, California October 1, 2013. (Photo by Robert Galbraith/Reuters)

Inmates walk in San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Tylan Gregory plays with his daughter Tyla, 5, during a “Get On the Bus” visiting day to Folsom State Prison arranged by the California Department of Corrections and Rehabilitation (CDCR) and the Center for Restorative Justice Works (CRJW) in Folsom, California July 26, 2014. (Photo by Elijah Nouvelage/Reuters)

Inmates participate in the workshop “Commedia Dell'Arte”, part of the The Actors' Gang Prison Project program at the California Rehabilitation Center in Norco, California September 30, 2014. (Photo by Mario Anzuoni/Reuters)

Inmate Donnell Moore touches the head of his son Donnell Moore during a special Father's Day visit part of the “Get On The Bus” program at California Men's Colony in San Luis Obispo, California May 30, 2015. (Photo by Mario Anzuoni/Reuters)

A woman sits in a cell at the Los Angeles County Women's jail in Lynwood, California April 26, 2013. (Photo by Lucy Nicholson/Reuters)

Inmate Jamar Allah flips his tassel as a graduate before receiving his High School GED (General Equivalency Diploma) along with 26 others at a graduation ceremony for inmates at the George Motchan Detention Center at New York City's Rikers Island correctional facility June 26, 2012. (Photo by Mike Segar/Reuters)

An inmate visits a dentist in the medical facility at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Prisoners work at computers following a graduation ceremony from a computer coding program at San Quentin State Prison in San Quentin, California April 20, 2015. (Photo by Robert Galbraith/Reuters)

A prison inmate works out at Oak Glen Conservation Fire Camp #35 in Yucaipa, California November 6, 2014. Thousands of convicted felons form the backbone of California's wildfire protection force under a unique and little-known prison labor program. (Photo by Lucy Nicholson/Reuters)

An inmate patient is shown in his cell at the California Medical Facility (CMF) in Vacaville, California, March 17, 2010. CMF was established to provide a centrally located medical and psychiatric institution for the health care needs of California's male felon population. (Photo by Robert Galbraith/Reuters)

San Quentin post office is seen outside San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

An inmate waits for a visitor at the California Institution for Men state prison in Chino, California, June 3, 2011. (Photo by Lucy Nicholson/Reuters)

Martell Collins, 51, does push-ups in the exercise yard at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Inmates sort laundry at the Orange County jail in Santa Ana, California, May 24, 2011. (Photo by Lucy Nicholson/Reuters)

The entrance to death row is seen at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Albert Ruiz, 50, who is on death row for murder, is led down a corridor at San Quentin state prison in San Quentin, California, June 8, 2012. (Photo by Lucy Nicholson/Reuters)

Prisoners walk in the exercise yard at San Quentin State Prison in San Quentin, California April 20, 2015. (Photo by Robert Galbraith/Reuters)