A convicted sex offender charged with first-degree murder in connection with the 2014 death of Jaimee Mendez pleaded guilty yesterday to voluntary manslaughter and was sentenced to 17 years behind bars, despite the objections of the Swampscott mother’s grief-stricken family.

Jason J. Fleury, formerly of Lynn, was scheduled to go to trial on April 3 in Salem Superior Court, where he could have been sentenced to life in prison without the possibility of parole if he had been convicted of the original charge — first-degree murder.

“I’m truly terrified about what will happen when this monster is back on the street,” Alyssa Mendez, the victim’s sister, told Associate Justice Thomas Drechsler as Fleury, 39, stared blankly ahead. “Today, your honor, you’re making a deal with the devil. … I wonder if he felt anything when he watched the life drain from her eyes.”

Assistant District Attorney John Brennan said there were questions that he believed could not have been answered had the case gone to trial.

As a result, both Brennan and Fleury’s attorney, Michael T. Phelan, recommended a sentence of 17 years — three years short of the maximum for voluntary manslaughter — a sentence that Drechsler accepted.

“I hear and feel the loss here,” the judge said. “But nothing I do or the commonwealth does is going to bring Jaimee Mendez back.”

Mendez, 25, was last seen Nov. 6, 2014, getting into a van consistent with the one Fleury owned, Brennan said.

When a friend of hers spoke to her by phone later that day, he said, she was scared and told him Fleury “seemed to be on drugs or all coked-out.”

In a dumpster outside a CVS in Lynn, Brennan said, Mendez’s sneakers were found, along with the van’s passenger side door panel and carpet, both of which had droplets of blood consistent with the victim’s DNA profile.

The day after she vanished, Fleury showed up at his landscaping job with scratches on his face and hands, the prosecutor said.

Fleury initially denied spending any time with Mendez but later said he had left her at CVS, Brennan said.

Cellphone records showed he had been in the Swampscott area the day she disappeared, he said.

For the next 83 days, police and Mendez’s family searched for her until a dog walker found her skeletal remains washed ashore on King’s Beach in Swampscott on Jan. 28, 2015.

An autopsy found the cause of death was homicide “by violent tendencies,” Brennan said.

Fleury was arrested that August in Hampton, Va., after an Essex County grand jury indicted him on a murder charge in connection with Mendez’s death.

Fleury is a Level 3 sex offender — the level deemed mostly likely to reoffend — who was convicted in 1997 of rape and abuse of a child in Virginia.