Thomas Montgomery, a 46-year-old balding husband and father of two (screen name: Marinesniper) had lied to beautiful 18-year-old Jessi (Screen name: Talhotblond) for more than a year.
Pretending to be a handsome 18-year-old Marine, he won her heart in cyberspace and, even though they had never met face to face, proposed marriage.
But it all came undone when his wife found a trove of love letters and sent Jessi a photograph of her husband and his family.
A furious Jessi then became involved with Montgomery's young co-worker and former friend Brian Barrett (screen name: Beefcake) -- a 22-year-old college student, studying to be a teacher. Like Jessi, he enjoys sports. Unlike Montgomery, he is real.
"He's honest, he wasn't a liar like you were," Montgomery said Jessi told him. "He's closer to my age."
Jessi began sending Barrett the same photos she'd previously sent Montgomery, along with cards that revealed deepening feelings: "My sweet Brian, I love you"
Montgomery became crazed with jealousy. "Brian will pay in blood," Montgomery instant messaged Jessi at one point.
His messages became increasingly violent, as he was forced to watch their romance blossom in the same chat rooms he used to frequent with Jessi.
"He was enraged," said former prosecutor Ken Case. " I mean, it oftentimes shocked me when I saw the names that he would call her."
Marinesniper: u r nothing and will be nothing but a lying whore
Jessi and Berrett took to the Internet to make sure everyone knew Montgomery (who recently had a birthday) was a liar.
"They were then going into these chat rooms, and letting people know that he was actually 47 years old," said Case. "They almost made him out to be a pedophile."
But the IMs that came from Talhotblond showed her to be torn --- mad one instant, desperate to return to a love with a man who she knew didn't exist ... teasing him.
She continued her talking to Montgomery online:
Talhotblond: i ache to be with tommy
Talhotblond: do you miss it tom
Marinesniper: more then u will ever know
Marinesniper: my heart aches to hear you call me your tommie
Marinesniper: i wish i could be that 19 yr old marine for u
Talhotblond: i know tom
Marinesniper: coming for u to run away with him
Talhotblond Rekindles Cyberaffair
Jessi took up with Montgomery again.
"In his mind, this was the jackpot," said Barbara Schroeder, who documented the bizarre relationship in a documentary called "Talhotblond." "He was being accepted for being 47, and he still had this hot young girl who wanted him."
Montgomery knew he was in way over his head, but he couldn't bring himself to end things with her.
"It was like a drug. I was addicted to it," he said. "I couldn't just, just end it."
At one point, when his wife actually told him to get off the computer and talk to her, Montgomery couldn't. "I just told her I'll get off when I'm done," he recalled.
Montgomery tried to break it off with Jessi more than once, but each time "talhotblond" pulled him back:
marinesniper: I have to leave honey
talhotblond: why tom
marinesniper: because i can never ever have u as i want u
talhotblond: dont go
marinesniper: y jessi u can get on with ur life then
talhotblond: i have no life
marinesniper: honey yes u do
talhotblond: my grades r dropping
talhotblond: i hate softball
talhotblond: i fight with my ma all the time
Montgomery says nothing sexual happened between them after she found out how old he was, but their IMs tell a different story:
marinesniper: wish you were nude
talhotblond: what would ya do?
talhotblond: that all
marinesniper: u might get the magic
talhotblond: make love to me tommy
'Marinesniper' Takes Revenge on 'Beefcake'
But it didn't last. Jessi told Montgomery they were through, and seemed to take up with Barrett again. Montgomery began to go into a downward spiral.
"The obsession turns into jealousy, and then the jealousy turns into betrayal and revenge," said District Attorney Frank Sedita. "You really start to get a, a sense of this person going into an abyss. And it's, it's kind of frightening."
And then ... the tipping point. Barrett said he was going to meet Talhotblond -- in person.
"He actually drove down to, I think North Carolina," said Case. "And on his way back, he was saying, 'I'm going right past your house. I'd love to get together.'"
Jessi texted him at the last minute not to visit, but Montgomery, who had learned of the plan to meet, was incensed.
On Sept. 15, 2006, as Barrett left work, three shots rang out. Brian Barrett was found dead in the parking lot where he worked, shot three times by a military rifle.
Police quickly learned of the Internet love triangle from co-workers. And when they couldn't find Thomas Montgomery, they feared they knew just where he was headed.
"At three in the morning," Capt. Ron Kenyon told "20/20," "our first concern was talking to Jessi and making sure she was still alive.
But when police arrived at her home, they were in for another surprise.
Brian Barrett's family has created a memorial foundation to raise awareness about the dangers of the internet. Click here to visit the Web site.