The Old Main prison south of Santa Fe is cold and dark, with rusty metal, broken glass and fire-stained walls where a bloody prison riot left 33 prisoners dead 32 years ago this week.

Just outside what once was the protective-custody unit, where most of the violence took place, are chop marks in the concrete floor where an inmate was beheaded.

Upstairs, you can see on the floor a dark fetal shape from a burned body.

Downstairs, in the basement, you'll find an array of execution devices no longer used by the state of New Mexico, which abolished the death penalty a few years ago.

During this centennial year of New Mexico's statehood, at the request of Gov. Susana Martinez, the state Department of Corrections will give free public tours of Old Main once a month.

The first scheduled tour, on Thursday, already is booked at maximum capacity of 100 people. But the tours will continue on the second Friday of each month, March through December. To reserve a place, contact department spokeswoman Rosie Sais at rosie.sais@state.nm.us.

During a news media tour Wednesday, Sais said the goal of the public tours isn't to focus on the 1980 riot, but to look at the history of prisons in New Mexico and progress that has been made.

"Back before the riot, there was overcrowding in the prison," she said. "The officers were not properly trained. There was no programming for inmates. ... We've now got [educational programs]. There's an academy set up for cadets to go to before they start work."

The tours begin in the lobby with a memorial to the five corrections officers killed in various state prisons before and after the riot. No officers were killed during the 1980 riot.

Nearby are displays of corrections officers' equipment, homemade weapons confiscated from prisoners, prison gang symbols and prisoner crafts, plus an exhibit of newspaper clips concerning the riot and its aftermath assembled by students at Moriarty High School.

A.B. Sena, 66, a retired corrections officer who was on duty in 1980, was among those answering reporters' questions on Wednesday. He said he doesn't spend a lot of time pondering the riot, but he sees nothing macabre about public tours of the old prison, since "it's part of our history."

Another retired corrections officer, Bob White, 61, recalled how he was living on the grounds of the Penitentiary of New Mexico on Feb. 2, 1980, when a neighbor woke him up at 2 a.m. to tell him inmates had control of the prison.

As a classification officer, White was familiar with the inmates in the protective-custody unit -- "snitches" who had testified against others, those with mental illnesses, and pedophiles and homosexuals who would be at risk with the general prison population.

At the time of the riot, the 90-cell unit held up to 200 prisoners, meaning some of the 9- by 6-foot cells held three prisoners at a time.

"When I came down here, I came with some trepidation," White recalled. "I was concerned about what I was going to find. When I walked in, here was smoke, water. The cell bars had been cut open. You could see where people had been beaten to death against the walls."

Lt. Vincent Vigil, who began his career as a corrections officer long after the 1980 riot, said the Old Main was state of the art when it opened off N.M. 14 in the late 1950s, replacing a prison that had been located on Pen Road, near Cordova Road, in Santa Fe.

It was built in a "telephone pole" style, with prisoner areas on cross structures connected by a long hallway that could be blocked by metal gates to isolate any disturbance. For unknown reasons, the gates were unlocked on the evening the riot began among prisoners drinking homemade alcohol.

The rioting prisoners took over the east end of the prison and quickly moved down the hallway to the control room, where they broke out glass panes and chased away guards. Then they moved to the west side, where they began killing inmates in the protective-custody unit. Not until two days later did the New Mexico National Guard put an end to one of the most violent episodes in U.S. prison history.

Most prisoners were moved to the state's other 10 prisons after the riot, although some inmates continued to be housed there until 1997. Since then, it has been used for storage and for movie sets.

Perhaps the eeriest part of the tour is a visit to the basement, where the gas chamber -- used only once in 1960 to execute murderer David Cooper Nelson -- is located. During the 1980 riot, two corrections officers hid inside the chamber and in a nearby storage cabinet.

Next to the gas chamber, in a room designed for use by witnesses to executions, state officials have arranged a display of other execution devices:

• A miniature gallows and hangman's noose, like those used to execute prisoners in the counties where they committed the crimes in territorial days, and for the first decade of statehood at the old prison.

• An electric chair used for executions from the early 1920s until 1960. The chair is the property of the Old Colfax County Courthouse Museum in Springer, which has loaned it to the Department of Corrections through 2012.

• A padded table with straps and intravenous equipment for lethal injections, used once on Nov. 5, 2001, on child murderer Terry Clark, the last person executed by the state of New Mexico.

New Mexico abolished capital punishment in 2009, although Gov. Martinez is seeking to reinstate it. Prison officials say if the lethal-injection table is needed again, it will be moved back to the nearby maximum-security prison complex.

Contact Tom Sharpe at 986-3080 or tsharpe@sfnewmexican.com.