Beliebers may start shrieking even louder than usual at this news -- and not for the right reasons, either: A convicted killer had a plan to castrate and murder Justin Bieber.

TMZ reports that convicted murderer Dana Martin, who is currently serving two life sentences in New Mexico for the gruesome rape and murder of a 15-year-old girl in Vermont back in 2000, reportedly asked fellow inmate Mark Staake to carry out the bizarre and horrific plot upon Staake's release. Staake is said to have asked his own nephew, Tanner Ruane, to help him carry it all out.

No one knows when the plan originally came up, but it was supposed to go down at Bieber's Madison Square Garden show last month.

Martin, who is obsessed with Bieber -- he even has the 'Boyfriend' singer's mug tattooed on his own leg -- told cops that he planned to strangle Bieber and Bieber's bodyguard with his trademark paisley ties, then have Ruane castrate the singer. For whatever reason, Martin told cops about the plan on his own, and thankfully so: Staake was arrested on outstanding warrants in Vermont before he could do much, and cops arrested Ruane, who'd made it to NYC with a bunch of scary tools (including pruning shears) before anything really scary went down. Yikes!

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