A former lieutenant at Brooklyn’s federal jail was convicted on Monday of sexually assaulting five female inmates, bringing a close to a yearlong prosecution that involved two other guards at the jail and exposed a pattern of abuse at the facility, the Metropolitan Detention Center.

After three days of deliberation, a jury in Federal District Court in Brooklyn issued a guilty verdict against the latest defendant, Eugenio Perez, 47. Mr. Perez was charged in May 2017 with forcing five female inmates at what is known as the M.D.C. to perform oral sex on him. The attacks took place, prosecutors said, in the lieutenant’s office on the second floor of the jail, where Mr. Perez was able to monitor security cameras to avoid being caught.

In closing arguments on Thursday, Nadia Shihata, one of the prosecutors in the case, said that Mr. Perez called himself “Caballo” (the Spanish word for horse) and treated his victims “like they were his stable.” Ms. Shihata added that Mr. Perez often chose vulnerable women to assault — some had been subjected to disciplinary measures, others were awaiting immigration proceedings — and used those vulnerabilities against them, warning that if they spoke of the attacks there would be further repercussions.

“He knew who to pick,” Ms. Shihata said, adding, “Who’s going to believe them?”

The assaults against the women, prosecutors said, took place intermittently from 2013 to 2016 and tended to follow a pattern. Mr. Perez would request that the women — all of whom testified under aliases at his trial — be placed on work details to clean the lieutenant’s office. Then, prosecutors said, he would expose himself to them, force them into oral sex and ejaculate into paper towels he eventually disposed of.