BIRMINGHAM, Ala. — Another inmate was stabbed in a prison yard at Alabama’s Elmore Correctional Facility, the third prisoner slain this year at the overcrowded and understaffed lockup, officials said Wednesday.

Timothy Robertson, 47, was fatally wounded Tuesday night. Another inmate, Jason Lee Jackson, 28, was being charged with murder, the Department of Corrections said.

Video surveillance and witnesses identified Jackson as a suspect after an officer found Robertson in distress in a prison yard, the statement said. Robertson was serving 35 years for rape. Jackson is serving five years for robbery.

Two other prisoners died in separate stabbings in February, and an officer was wounded in a stabbing in March at the medium-security lockup north of Montgomery.

Prison Commissioner Jeff Dunn said the agency is assessing all of its maximum- and medium-security facilities to determine where “critical staffing” is needed.

“The safety of our officers and those in our custody is our utmost concern, and we will employ all available resources to prevent the escalation of violence in light of recent incidents,” Dunn said in the statement.

In all this year, four homicides have happened in Alabama prisons, including one at nearby Staton Correctional Facility, and officers have been injured in six assaults, prison spokesman Bob Horton said in an email interview.

Officials don’t know of any single reason Elmore has a higher homicide rate than other state prisons, but the facility is badly overcrowded and understaffed.

Elmore has only 72 of the 169 officers it is authorized to employ, yet the prison population is at 190 percent of its designed capacity with 1,145 inmates, Horton said. As a result, inmates are packed into huge dormitories with limited oversight.

“The inmates are double-bunked and an officer’s line of sight inside the dorms is limited, which can lead to a higher risk of violent activity,” Horton said.

State lawmakers have refused proposals to construct new prisons, and administrators say low pay and dangerous working conditions make it difficult to hire and retain officers.