The title of this fascinating true-crime documentary from upstate New York is a screen name: “talhotblond” meaning a tall, hot blonde, all of 18 years old. And her sexy jailbait photos are posted while trolling game rooms, leading to cyberchat and more. The guy who falls for her goes by the handle “marine sniper,” since he was actually once in the Marines, but two decades earlier–before wife and kids and a factory job. Their correspondence makes him feel young, so he tells her he’s also 18, and soon to be deployed to the Iraq War. And from there, deception leads to tragedy. The guy, Thomas Montgomery, is pictured at right; and he’s interviewed extensively in Barbara Schroeder’s sneaky, remarkable, spoiler-filled debut documentary. Sharp-eyed newspaper readers may recall the case from early 2007; it’s perfect for 20-20 or America’s Most Wanted, though the networks seem to have skipped the story after its speedy courtroom trial. (There, the judge calls it “a love triangle between three people who did not ever know each other.”) But Schroeder, using the voice of the murder victim to narrate (clearly identified as a device), gains remarkable subsequent access to the cops, prosecutors, and families of the three main parties involved. She fills the screen with IMs and sex-texts taken from court evidence, snapshots, and home movies. What emerges is a shocking tale of cyber-deception and sad, middle-aged self-delusion only made possible by the Internet. One qualifer: The score and cheesy A Current Affair-style sound effects are terrible, and should be replaced before talhotblond reaches cable, theaters, or DVD. Otherwise, it’s one of the best movies I’ve seen at SIFF this year. talhotblond Pacific Place, 9:15 p.m. Fri., June 12 and 4 p.m. Sat., June 13.