Murder of Gary and Jan Tyrrell by Mark Porter examined on A Time To Kill

Mugshot of Mark Porter
Mark Porter pleaded guilty to killing Gary and Jan Tyrrell. Pic credit: MO Dept. of Corrections

A Time To Kill is investigating the 2014 murder of husband and wife, Gary and Jan Tyrrell, who were murdered by their so-called friend, Mark Porter.

Porter had been having financial difficulties due to a gambling problem and decided that his best way out of trouble would be to steal from and murder the Tyrrell couple at their home in Springfield, Missouri.

In May 2014, Jan and Gary Tyrrell’s daughter contacted the police after she had trouble reaching her parents. When the cops investigated their home, they found that the couple had been murdered; 60-year-old Gary had been shot twice, and 61-year-old Jan had suffered a blunt force trauma to the head.

Gary Tyrrell had been an avid trader and collector of precious metals and rare gemstones, and their house was full of these valuable items, and someone had attempted to break into their safe. But the police found no sign of forced entry leading them to believe this was not a simple case of a robbery turned violent.

Mark Porter became murder suspect no.1

The police turned their focus to family friend and colleague Mark Porter, who worked with Gary in his position as a superintendent at the Mountain Grove School District, MO. Gary had been his assistant and long-time friend, and Porter was one of the few people who had been allowed into the Tyrrell home.

The investigators learned that Porter had a gambling problem and was in financial difficulty at the time of the murder and that he had asked Tyrrell for a loan worth $250,000, which was refused.

The detectives then found that Porter had sold $18,531 worth of silver coins days after the couple’s deaths. The cops also discovered documents at the Tyrrell home which stated they owned a collection of silver coins worth approximately $22,000.

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However, it was DNA evidence that finally confirmed that Porter was behind the murders. The killer’s DNA was found on a latex glove left near Jan’s body, and an undercover cop later retrieved DNA from a coffee cup discarded by Porter. It was a match.

Porter was charged with murder, and in 2015, he pleaded guilty to two counts of second-degree murder and was sentenced to life in prison. His guilty plea meant he avoided the death penalty.

More from A Time To Kill

Follow the links to read about more murders profiled on A Time To Kill.

Cleo Hines and Paul White burst into the office of Robert Eidman in St. Charles, MO., and demanded money. They stole his wallet and shot him three times in the head and neck.

Paige Birgfeld was leading a secret double life as an adult escort when one of her clients, Lester Ralph Jones, abducted her and murdered her in a secluded area near Grand Junction, Colorado.

A Time To Kill airs at 9/8c on Investigation Discovery.

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