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Investigators have confirmed that the prison death of convicted murderer Martin MacNeill in April was a suicide, according to recently released investigative reports.

MacNeill, 61, died on April 9 at the Utah State Prison, where he was serving a lengthy sentence for killing his wife, Michele MacNeill, and sexually assaulting their adult daughter weeks after his wife's death.

The former doctor was found deceased by two prison inmates near a greenhouse in the Olympus section of the prison, a Unified Police report released Friday states. Investigators wrote that it appeared as if MacNeill killed himself by using a plastic bag and a hose attached to a natural gas line meant for a heater inside the greenhouse.

Officials noted that MacNeill — who was authorized to work in the greenhouse — did this in an area where he could not be seen, and that it did not appear that there was a struggle, an indication that MacNeill ended his own life.

The two inmates who found MacNeill told investigators that they thought the man had killed himself because he had just lost a court appeal, according to the report. One inmate said MacNeill told him he was "tortured" by suicide-watch protocols the last time he tried to kill himself behind bars, and he said if he ever tried again, he would never tell anyone.

MacNeill attempted suicide at the Utah County jail in November 2013, a month after a jury found him guilty of first-degree felony murder and second-degree felony obstructing justice in his wife's death. He had tried to cut his femoral artery with a disposable razor and, as a result, was on suicide watch until he was sentenced to the prison in September 2014.

MacNeill's death came several weeks after the Utah Court of Appeals ruled that there was enough evidence presented at his high-profile trial to convict him of killing his wife.

On April 11, 2007, Michele MacNeill, 50, was found unconscious in her bathtub at the couple's Pleasant Grove home by her then-6-year-old daughter and was taken to a hospital, where she was pronounced dead.

At trial, prosecutors presented a theory that Martin MacNeill gave his wife a fatal cocktail of prescription drugs and then drowned her so he could continue an affair with another woman. The defense countered that MacNeill was at work at the time of his wife's death and said there was reasonable doubt of his guilt, pointing to circumstantial evidence and an inconclusive autopsy.

MacNeill also was convicted of second-degree felony forcible sexual abuse in a separate case of inappropriately touching his adult daughter weeks after Michele MacNeill's death. He lost an appeal in that case, too, after the Utah Court of Appeals rejected his argument that the high-profile murder trial tainted his chance to get a fair trial in Utah County.

He was not expected to get his first bid for parole until August 2052 — when he would have turned 96 years old.

Twitter: @jm_miller