"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: A woman named Mary Shieler opened the door.
As police questioned her, she revealed a shocking truth: She was the one who had been sending messages to Montgomery and Barrett under the handle Talhotblond. The pictures she sent Montgomery were actually those of her daughter, the real Jessi, who had no knowledge of her mother's cyberlife.
Montgomery was charged and later plead guilty to the murder of Brian Barrett. In exchange for his plea, he received a 20-year sentence. Prosecutors said their discovery of Montgomery's DNA on a peach pit found at the crime scene and a photo of Montgomery family's gun cabinet -- which showed the type of old military rifle that police believe was used to shoot Barrett -- were key to their case against Montgomery.
Prosecutors in Buffalo, meanwhile, looked for a way to charge Mary Shieler for something -- anything -- in the case but concluded she may have tramped all over the moral and ethical line, but never crossed the legal one.
"Shame on her -- she not only didn't do anything about it, I think she provoked it," said Ken Case. "Unfortunately in New York State, you have to do a little something more to be criminally liable."
Mary Shieler didn't come away unscathed. Her husband divorced her over her deception and her daughter Jessi cut ties too, moving in with relatives in Virginia, where she was attending college.
Mary Shieler also pursued an education -- she took classes at a community college in West Virginia. She has spoken publicly about the deadly love triangle just once, to the BBC.
"It was stupid. It should have never happened. I just never thought it would go anywhere," she said. "That it would end, fall off and that would be the end of it."