Law enforcement say two career criminals allegedly plotted to castrate and murder JUSTIN BIEBER.

Two ex-cons, Mark Staake and his nephew Tanner Ruane, planned to kill Bieber during his performance in New York at Madison Square Garden in November, court papers filed in New Mexico charge.

The two sickos allegedly hatched the nauseating plot after Staake met convicted killer and an over-the-top obsessive Bieber fan Dana Martin during a sentence in a New Mexico state prison.

Martin, who has a tattoo of Bieber adorning his leg, was convicted of raping and murdering a 15-year-old girl in Vermont in 2000.

Martin orchestrated the slay plot and reportedly told police the plan was to kidnap Bieber and his bodyguard and strangle them with paisley ties – Martin's calling card.

Ruane was then going to castrate them  – for $25,000 per testicle.

According to the court documents, police collared on outstanding warrants Staake and Ruaneon who were traveling to Vermont, according to court papers.

Investigators found pruning shears in wanna-be hit men’s vehicle.

Troopers recovered tools and documents associated with the conspiracy while executing a search on Ruane’s 1983 BMW,” NY State Police said. “The documents included the identities of the intended victims, their family members and their whereabouts.”