MINEOLA, N.Y. (CBSNewYork) — The trial for a Rockville Centre officer facing assault and other charges in connection with an altercation with two brothers outside a bar started Wednesday.

Cell phone video at the center of the investigation shows 37-year-old Officer Anthony Federico and Kevin and Brendan Kavanagh, brothers from a reputable Rockville Centre family, getting physical in May 2016.

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But what the video doesn’t show is who started the fight.

“He was on patrol that night, went to investigate a disturbance, and was attacked and defended himself,” Police Commissioner Charles Gennario said on Wednesday.

The veteran officer has been adamant about his innocence and said he was on-duty responding to a bar brawl alone when he claims he was pounced on by violent drunks. Federico’s lawyer says seconds before the video starts Kevin Kavanagh struck him in the face and refused orders, lunging at officer Federico.

Federico discharged his Taser several times before hitting Kevin Kavanagh in the head with the device, prosecutors said. The victim needed sutures and 15 staples to close up the six-centimeter gash.

The prosecutor told the judge that Federico acted out of vengeance and anger as the trial got underway in a Mineola courtroom Wednesday.

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Federico’s attorney William Petrillo said outside the courtroom that the officer acted lawfully and defended himself.

“This is a great police officer who the evidence is going to show reacted appropriately and professionally in a most dangerous situation that happened in seconds,” Petrillo said.

“You are looking at a police officer who lost control. He just lost it,” Joseph Dell, the attorney for the Kavanagh brothers, told CBS2 in April 2017.

Both brothers were arrested after the incident.

Officer Federico was indicted for assault and falsifying a police report.

The 37-year-old husband with a young son has been placed on modified duty, and faces up to seven years in prison if convicted. Commissioner Gennario says 15 cases in which Federico made arrests have been dismissed because of the current indictment.

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It will be a bench trial so a judge ultimately decides the outcome of the case, CBS2’s Carolyn Gusoff.