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The Sunday death of Utah State Prison inmate Martin Joseph MacNeill, a former physician who murdered his wife in 2007, is being investigated as a suicide, authorities announced Tuesday.

The Department of Corrections and the Unified Police Department said in a joint news release that the preliminary investigation shows no signs of foul play. The Office of the Medical Examiner will determine an official cause of death, which likely will take 10 to 12 weeks, and the investigation will remain open until then, according to the release.

Correctional officers found MacNeill unresponsive at 11:23 a.m. Sunday in the yard of the Draper prison's Olympus facility, according to the DOC. The 61-year-old could not be revived and was pronounced dead at the prison at 11:50 a.m.

MacNeill, a Utah County doctor who also had a law degree, was serving a sentence of up to life in prison for killing his wife. Michele MacNeill was found unconscious in the bathtub of the couple's Pleasant Grove home on April 11, 2007, and was taken to a hospital, where she was pronounced dead.

An autopsy ruled the 50-year-old woman died of natural causes, the result of heart inflammation and high blood pressure. But Michele MacNeill's relatives pushed authorities to investigate further and the then-doctor was charged with first-degree felony murder and second-degree felony obstruction of justice in 2012.

Prosecutors argued at a 2013 trial that MacNeill gave his wife a deadly mixture of prescription pills after she came home to recover from plastic surgery, then drowned her so he could continue an affair.

He was convicted of both counts by a 4th District jury and sentenced to prison terms of 15-years-to-life and one-to-15-years, which were to run consecutive to a one-to-15-year prison sentence MacNeill had received in a separate case for inappropriately touching his adult daughter.

MacNeill's appeals in both cases were turned down and his first parole hearing was scheduled for August 2052, when he would have been 96 years old.

The Olympus facility where he was housed is designated for inmates with mental health needs, according to the DOC website.

Twitter: @PamelaMansonSLC