LIMESTONE COUNTY, Ala. (WHNT) — A 42-year-old inmate serving a life sentence for a 2009 double homicide in Lauderdale County has died, according to the Alabama Department of Corrections (ADOC).

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Jonathan Cossey was found unresponsive in his cell in the Limestone Correctional Facility on Thursday, August 11, ADOC says.

Staff at the prison immediately began life-saving measures and transported Cossey to the health care unit, where ADOC says those measures were unsuccessful and he was pronounced dead.

On September 2, 2009, Cossey was accused of shooting and killing 30-year-old Selvia Yvette Martin Mitchell and 49-year-old Rickey Wayne Waller during a robbery at a home on Baker Point Lane in Florence.

At the time of their murders, Cossey was 29.

According to an article from the TimesDaily, Cossey was found in his pickup truck that was parked on a rural road in Hardin County, Tennessee. He was unconscious from a drug overdose.

Cossey pleaded guilty to two counts of capital murder in August of 2011. In the plea agreement, he was sentenced to life in prison, avoiding the possibility of being sentenced to death or life without parole.

Officials say that a cause of death is pending the results of a full autopsy. The ADOC Law Enforcement Services Division is investigating Cossey’s death.