A man from upstate New York has been sentenced to 20 years in prison for killing a co-worker in a fit of jealousy over a middle-aged woman in an online relationship who pretended to be 18.

Thomas Montgomery, 48, was sentenced earlier this week after he pleaded guilt to killing 22-year-old co-worker, Brian Barrett outside a Dynabrade tool factory where the two men worked.

The motive was an online relationship Montgomery established with a West Virginia woman, identified in court and by prosecutors as Mary Sheiler. Montgomery and Sheiler, who were miles apart and had never met, both came up with the same idea: to get online and pretend they were about 30 years younger than they actually are. They found each other on the Web and fell in love with each other's fake personas -- which were closer to their children's ages than their own.

Sheiler reportedly used pictures of her daughter to pretend she was 18 and flirted with Montgomery, who pretended he was a young U.S. Marine bound for Iraq. She mailed photos and lingerie to his home outside of Buffalo, and exchanged steamy messages online.

Montgomery's wife intercepted a package, according to local media reports, returned the favor with a note explaining that the tool factory worker was a married man in his late 40s, with two teenage daughters.

Sheiler, who had used the name "Jessica" online, knew the name of Barrett as one of Montgomery's co-workers at Dynabride and contacted him online to confirm the facts. She continued exchanging e-mail messages with Montgomery and Barrett at the same time. Both men apparently continued to believe the middle-aged woman was an 18-year-old.

Neither man ever met Sheiler, but Barrett ended up dead over the passions aroused by the older pair's deceit.

Barrett, a Buffalo State College student, was found dead from gunshot wounds inside his truck, which he had parked outside the tool factory.

Although Montgomery pleaded guilty, he later tried and failed to rescind the plea and is expected to appeal the case.

Erie County Assistant District Attorney Frank Sedita named old-fashioned jealousy the motive. But, this time, it definitely had a modern twist.

"You can pretend to be whoever you want to be on the Internet," he said in an interview Thursday. "And people will do and say strange things to represent who they are. I certainly don't do any Internet chatting."