The feds provided a vivid, blow-by-blow account Monday of the broad-daylight ambush shooting of an FBI agent in Brooklyn.

Reputed Crips gang member Ronell Watson drove a BMW M5 the wrong way on Canarsie Road and blocked in the agent’s car, got out, went up to the driver’s-side door and began blasting when the agent tried to get away, court papers say.

The unidentified agent was hit “by at least one round and suffered a gunshot wound to his torso,” but got out of the car and returned fire, hitting Watson at least once before Watson hopped back in the BMW and drove off.

Law enforcement sources have said the agent and two other feds in his car were conducting a gang-related stakeout at the time of the shooting Saturday afternoon.

Watson dumped the car at a nearby auto-body shop and later showed up for treatment at Kingsbrook Jewish Medical Center, where he claimed to have been an innocent bystander shot during a gunfight, according to the feds.

But law enforcement officers overheard him call his live-in girlfriend, Molissa Gangapersad, and tell her to go to their house and “get the jewelry and get rid of it,” court papers allege.

When FBI agents went to interview Gangapersad, she allegedly claimed not to have seen the shooting — but the feds say she changed her tune when she was confronted with surveillance video that shows her on the front porch of their house, with a clear view of the incident at the time it occurred.

A search of their home allegedly turned up 1 and a half pounds of pot, $15,000 in cash and “large amounts of jewelry” stashed in their bedroom.

Brooklyn US Attorney Richard Donoghue personally appeared in court Monday to successfully argue that Watson should be held without bail, calling him “a gun-wielding, drug-dealing gang member who shot an FBI agent in broad daylight.”

Donoghue said the evidence against Watson includes multiple videos of the shooting.

Law enforcement sources have said that Watson was driven to the hospital by Hector Amissah, 31, who wasn’t charged on Monday.

The Brooklyn US Attorney’s Office wouldn’t say why or whether Amissah was cooperating with authorities.

Gangapersad was released on $500,000 bond, but neither she nor any of the defense lawyers in the case would comment.

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