Owner, company guilty in case of two workers who drowned in South End trench in 2016

Kevin Otto listened to discussion about his sentencing date after he was found guilty of manslaughter.Pat Greenhouse/Globe Staff

A Suffolk Superior Court judge convicted a drain company owner of manslaughter Thursday in connection with the 2016 deaths of two workers who drowned in a flooded trench at a job site in Boston’s South End.

Relatives of the victims rubbed one another’s shoulders and dabbed tears as Judge Mitchell H. Kaplan’s guilty verdicts were announced in the closely watched case against Kevin L. Otto .

Otto, 45, and his company, Atlantic Drain Service, were both found guilty of two counts each of manslaughter and one count each of witness intimidation. The defendants had opted for a bench trial.

Otto was at the job site on Dartmouth Street on the afternoon of Oct. 21, 2016, when a 14-foot trench quickly filled with water after a hydrant collapsed. Fifty-three-year-old Kelvin Mattocks and 47-year-old Robert Higgins were submerged and drowned.

After the verdict was rendered Thursday, Mattocks’s sister, Melinda Mattocks Ushry, said outside court that the resolution brings “a lot of closure” to her family and that it was “very hard” to relive the wrenching details of the case at trial.

District Attorney Rachael Rollins, who was in the courtroom Thursday, said after the hearing that she offered condolences to the victims’ families and hoped the conviction would “allow them in some small way to move toward the process of healing.”

Family members of Robert Higgins reacted to the verdict, including his stepfather Gerald Biancuzzo, mother Joyce Biancuzzo and aunt Debbie Aguiar.Pat Greenhouse/Globe Staff/Globe Staff

Otto left court without commenting, and his lawyer, Aviva E. Jeruchim, said via e-mail, “We are obviously deeply disappointed with the verdict. We’re considering our post-conviction remedies.”

Rollins’s office said Otto knew he was supposed to install cave-in protections known as trench boxes at the site, but the necessary safeguards weren’t present when dirt caved in, burying his workers up to their waists.

He shouted “get the hell out of the hole” to the pair, prosecutors said, but then the hydrant collapsed, unleashing a torrent of water that killed the two men.

Prosecutors said OSHA had informed Otto at job sites in 2007 and 2012 that he needed to install cave-in protections in trenches deeper than 5 feet.

Otto’s lawyers had argued that the government couldn’t prove the lack of a trench box caused the hydrant to collapse. The city is responsible for installing hydrants, which are supposed to be equipped with devices called thrust-blocks to keep them stable, but there’s no evidence such safeguards were ever placed on the hydrant in question, the defense maintained.

Kaplan, in delivering his verdict Thursday from the bench, said Otto took no steps to support the hydrant and other items, including the piping, prior to the trench collapse. Otto failed to take “reasonable steps” to prevent the tragedy, he said.

Kaplan declined a prosecution request to sentence Otto on Friday to accommodate victims’ relatives who had traveled to Boston from out of state with the hope of addressing the court at sentencing, which was scheduled for Dec. 4.

Kaplan said the case is different from most manslaughter trials in which victims are shot, stabbed, or beaten, and he’ll need to carefully weigh information submitted by both sides ahead of sentencing.

“I don’t think I can short-circuit that process,” he said.

Otto faces a maximum prison term of 20 years on each manslaughter count. State law says a company convicted of manslaughter faces a fine of up to $250,000, and that authorities “may debar the corporation . . . for a period of not more than 10 years.”

Otto remains free pending sentencing.

Melinda Mattocks Ushry talked with an assistant district attorney about t a date for sentencing. She is the sister of Kelvin Mattocks.Pat Greenhouse/Globe Staff/Globe Staff

Rollins said the victims’ relatives deserve to have prosecutors seek “a large amount” of prison time for Otto, but she declined to be more specific.

“I would be very surprised if my team suggested something different from that,” she said.

Rollins credited her predecessor, Daniel F. Conley, for initially bringing the manslaughter case against Otto and his company. While it’s a “novel thing” to charge a company with manslaughter, Rollins said, “I firmly believed it was the right thing to do.”

Camille F. Sarrouf, a lawyer for Atlantic Drain, declined to comment on the verdict outside the courthouse Thursday, except to say that “we already said our apologies to the families before,” and that “we just have to let justice prevail.”