A man pleaded guilty Thursday for his role in a 2015 boating mishap in the Boston Harbor that severed a young woman’s arm.

Alexander Williams, 26, admitted to negligent operation of a boat, furnishing alcohol to minors and tampering with evidence.

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“He's incredibly sorry for what happened out there, it was a tragic accident,” said Rob Goldstein, Williams’ attorney.

Williams, a former law intern, and his boss at the time, Ben Urbelis, were two of 13 people aboard the 30-foot vessel “Naut Guilty” on May 30, 2015. Prosecutors said that Williams brought along “enough liquor to kill a horse”, a direct quote from the defendant. Six of the passengers were women under 21, including the then-19-year-old victim, Nicole Berthiaume.

The district attorney says that while on the boat Berthiaume and others jumped into the waters near Spectacle Island. Williams, who prosecutors said didn’t know how to drive boat started the engine, but didn’t place it in neutral. Berthiaume was pulled underwater by the propeller, cutting off her right arm and lacerating her left arm, legs, abdomen and back.

Berthiaume spoke to the court last week and Suffolk Superior Court Linda Giles said it was “among the most moving impact statements I have ever heard in my 25 years as a judge.”

“I am a strong independent person; that’s something that has not and will never change. I don’t want help from other people, I don’t want people to think I am incapable of anything. I would rather struggle putting on a coffee coozie at Starbucks for 10 minutes and spill it everywhere when I open my car door than have anyone over me help. But to the world I am a damaged disabled person, so most times I will sacrifice my own pride and kindly accept the unwanted help, even though that itself is the most debilitating part,” Berthiaume said.

“You will rarely hear me complain about the incident, and you will almost never hear me complain about my disability, but that does not mean that it doesn’t kill me every time I look in a mirror, drop something, or accept help from someone.”

Williams struck a deal, pleading guilty to three charges in exchange for the case being continued without a finding for a two-year probationary term. Judge Giles ordered him to pay $5,000 for restitution, complete a certified drug and alcohol awareness program and perform 200 hours of community service at the Spaulding Rehabilitation Center or similar facility.

Berthiaume said she didn’t want to comment further after court.

Urbelis, who also owns nightclubs, is charged related to the incident and the case is expected to go to trial later this year.