"It comes as a surprise because he was not a noncompliant person," he said. "This is not somebody I would worry about doing something to anybody."
Carpenter was sentenced to life in prison in June 1983 for the 1982 murder of his 77-year-old grandmother with whom he lived.
Vada Viola Carpenter's body was found wrapped in bedclothes and covered with cedar branches near the C&O Canal National Park on Dec. 5, 1982.
She had been shot once at close range with a shotgun as she lay sleeping on Nov. 28.
Carpenter, who had fled to New York State after the killing, was returned to Clear Spring by relatives and led police to the body after confessing to the murder.
Although he confessed to the crime, Carpenter never gave a reason for his actions. Richards said a motive emerged through years of counseling.
"We wouldn't release anyone who we didn't know why they did it," he said.
Richards said state law prohibits revealing why Carpenter shot his grandmother, but he stressed that authorities determined the reason was related to a unique set of circumstances. He said the reasons could not be repeated.
At the time, Maryland State Police investigators learned that earlier on the night of the shooting, Carpenter's grandmother had refused to take a family pet to a veterinarian after it was struck by a car.
The Patuxent Institution, located in Jessup, Md., provides intensive psychiatric treatment to about 350 inmates and serves another 100 in its youth program. Although run by the state, it is separate from the Division of Correction and has its own paroling authority, a panel appointed by the governor.
Cindy Reisberg, a spokeswoman for the facility, said Carpenter became eligible for parole in 1993. She said parole requests must be made by therapists at the institution and approved by Board of Review. She said, however, that had not happened.
Richards said inmates progress through four stages before being allowed unsupervised visits. Inmates in Level 1 live in double cells and are allowed minimal phone and visitation privileges. Through good behavior and psychiatric improvement, prisoners are able to move up.
As the levels advance, so do privileges like phone use and movement throughout the facility. By Level 4, inmates usually have their own cells and wide freedom to move around the facility, Richards said. He said they also regulate many of their activities.
After successfully completing all four levels, inmates can win work-release privileges, he said. They also can win leisure passes, first supervised by corrections officers and then unsupervised.
Richards said Carpenter advanced through the stages more slowly than typical inmates because of the severity of his crime.
Richards said the institution averages about one walk-off every two years, but most gain little attention because the inmates committed nonviolent offenses. He said it is extremely rare that a murder convict would be allowed to leave the facility.
"It is not common - not at all. There are very few people who have that status," he said.
He said there currently are only four inmates serving life sentences who have the privilege and another five or six who are serving suspended life terms.
But he said Carpenter has been a model prisoner in every way and had no prior criminal history before being charged in his grandmother's death. He said he has never committed an offense against a staff member or another prisoner.
Richards said years of analysis and common sense have led therapists to conclude that Carpenter's actions were an aberration.
"Basically, it's a family tragedy," he said.
Carpenter has been eligible for work release since February 1995. He has been working for a Baltimore lumber yard for several months, Richards said. He added that Carpenter has been given overnight passes on weekends since last then Nov. 21.
Carpenter is about 5 feet, 6 inches tall, weighs 115 pounds with a medium build, medium complexion, brown eyes and black hair.