Dwayne Matthew Samson was charged with second-degree murder in the death of 43-year-old Boudreau in 2013.
Eleven days were set aside for the trial Port Hawkesbury, but on Tuesday, the Crown said it intended to proceed with a manslaughter charge.
According to an agreed statement of facts read in court, the crew of the Twin Maggies saw Boudreau at their traps that day and believed he was tampering with them.
They loaded a gun, and Samson asked Landry to shoot at Boudreau. One shot him in the leg.
According to the statement, which Samson agreed to, they ran at Boudreau's boat several times.
Samson was at the wheel when Boudreau fell into the water. They then gaffed Boudreau and dragged him out to sea.
At some point, Boudreau stopped struggling.
A jury has already found fisherman James Joseph Landry guilty of manslaughter. He had been charged with the more serious charge of second-degree murder in a case that's been dubbed "murder for lobster."
Two other crew members aboard the Twin Maggies boat also face charges connected to the disappearance of Boudreau, whose body has never been found.
Samson's wife, Carla, owner of the lobster boat and Landry's daughter, faces a charge of accessory after the fact. Craig Landry, a third cousin of James Landry, is charged with accessory after the fact.
Samson will face a sentencing hearing Aug. 11 and 12. He is allowed to return to D'Escousse to live until then.
The defence says it wants to put forward physiological evidence.
The CBC's Wendy Martin is live tweeting from the trial.