A Suffolk County police detective who posed as hit man "Bobby Russo" testified that a sidekick of convicted coin fraudster Joseph Romano offered him $20,000 apiece to behead a judge and prosecutor at Romano's murder conspiracy trial in federal court in Brooklyn Monday.

Det. Robert Strecker said Romano first asked for a Long Island car mechanic who he hated to be beaten, and after the FBI staged that assault he quickly escalated to the murder of Central Islip U.S. District Judge Joseph Bianco and prosecutor Lara Gatz.

"He wants like Blanco, an accident, whatever, doesn't matter," said Romano pal Dejvid Mirkovic, who mispronounced Bianco's name throughout a recorded 2012 meeting in the undercover detective's car in a Home Depot parking lot in East Meadow.

"Gatz you gotta make disappear," he said. "He wants her in a 35 gallon drum. Not a 50. A 35 gallon drum."

Romano, 50, of Levittown, is being tried on charges of plotting the death and mutilation of the judge and prosecutor in revenge for a 15-year sentence in a coin-fraud case. He tried to orchestrate their killings from the Nassau County jail. Mirkovic has pleaded guilty.

During the conversation in the car, he shares personal details of the targets with "Bobby" to help pull off the hit. He tells him Bianco drives a Porsche, and when the hit man worries Gatz might be too big to stuff in the drum, Mirkovic reveals she's 5-foot-5.

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"She should fit," he says.

"Bobby" takes it in stride when Mirkovic tells him the heads of the victims are to be preserved in formaldehyde. Later, he tells the hit man that Romano wants other body parts removed, too.

"That's freaky," replies the undercover officer.