Aug. 27, 2011 — -- The Internet is known as a breeding ground for illicit affairs between people often hiding behind fake names and handles. But most such virtual relationships aren't dangerous as this -- when "Talhotblond" and "MarineSniper" struck up a relationship online, it ended in murder.

MarineSniper was 46-year old Thomas Montgomery, a married father of two. In May, 2005, posing as a young, handsome Iraq-bound Marine, he entered a teen chat room the popular game site "Pogo."

When 18-year-old Talhotblond started instant-messaging him, he decided to pretend he was 18 too.

"I kept thinking, well, we're never going to meet. ... I'll just play the game with her," he said.

Before long, the flirtation became a romance.

Talhotblond's instant messages revealed that her real name was Jessi, a softball-playing high school senior from West Virginia. She sent Montgomery photos that lived up to her screen name ... and then some.

"There were some ... very provocative poses," he said.

In return, Jessi wanted to see what he looked like too; so he sent her his photo from Marine boot camp.

The picture was 30 years out of date. Montgomery's screen name, Marinesniper, was a nostalgic harkening back to the six years he spent in the military as a young man.

He has hinted darkly of covert ops and dark deeds best unmentioned, but U.S. Marine records obtained by "20/20" show that although he qualified as a sharpshooter, he never trained as a sniper or saw action.

But for Jessi, he invented a younger, stronger, more virile version of himself, called "Tommy." "He was my height, 6 feet tall, had bright red hair," said Montgomery, "big shoulders, muscles and all that."

Instant messages recovered from his computer show that the online relationship began to consume Montgomery. He told "20/20" that this relationship "became more real to me than real life."

The feeling seemed to be mutual. Jessi and "Tommy" exchanged gifts, phone calls and love letters.

"I love you always and forever, Tommy," wrote Jessi.

"I have never felt this way," Montgomery responded.

The relationship had become more than a flirtation, Montgomery said.

"There was virtual sex going on in there between her and Tommy," he said.

While Montgomery said the virtual sex made him "feel kind of dirty," he was in too deep to sever ties with her.

"If I was smart, I would've just ended it, but it was like a, a drug that I needed every day," he said.

Montgomery seemed to be losing touch with reality. He wrote a note to himself: "On January 2, 2006 Tom Montgomery (46 years old) ceases to exist and is replaced by a 18-year old battle-scarred marine ... He is moving to West Virginia to be with the love of his life."

ncG1vNJzZmiZkpi7psPSZ56oZpOkunChsmimp6SZo7JuuM6vnGasop6ur7PLnmSdnZOavbW1zqdknqaUYrq2vsOeqWirpKS%2FuovInXRqbGNsfnGDlQ%3D%3D