A 13-year-old boy whose body was found buried off a rural highway in New Mexico had endured years of abuse that included being locked for hours inside a dog kennel, authorities said Tuesday.

Santa Fe County Sheriff Robert Garcia choked back tears as he provided more details about the case that authorities described as gruesome and heartbreaking.

“I can honestly say this poor child suffered at the hands of a monster,” the sheriff said of Thomas Wayne Ferguson, who was dating the boy’s mother and has an extensive criminal history, including for child abuse.

Garcia said at a news conference that he was awaiting the results of an autopsy to determine how Jeremiah Valencia died and the extent of the boy’s injuries.

Investigators on Monday announced the arrests of Ferguson, 42; the boy’s mother, Tracy Ann Pena, 35; and Ferguson’s son Jordan Anthony Nunez, 19, in connection with Valencia’s death more than two months ago.

All three are jailed on suspicion of child abuse resulting in death, tampering with evidence and conspiracy to commit tampering with evidence. It wasn’t immediately clear if they had attorneys.

Ferguson told investigators that Valencia died after he and Nunez had been roughhousing, according to court documents. However, Nunez said he saw his father punching the boy in the face and stomach multiple times on Nov. 26. Nunez said the boy was bleeding and that Ferguson put padlocks on all the doors in the house to make sure no one left.

Pena told investigators that when she got out of jail on Nov. 26, she went home to find her son’s body wrapped in a blanket. After confronting Ferguson, she said he put the body in a vehicle and drove away.

She told authorities she was scared of Ferguson and that he had physically abused the boy in the past. She said Ferguson later took her to a spot where the boy was buried, a location she shared with authorities.

Authorities say the family was able to conceal the boy’s death because he was not enrolled in school and had never been reported missing.

The investigation began last week when authorities received confidential information about a possible homicide from an inmate who was in jail with Pena. The inmate told authorities Pena had talked about finding her son dead and blamed Ferguson, who also was in jail at the time on a probation violation.

Authorities said Nunez, who is also identified in court documents as Jordan Munoz, reported growing up in a “very abusive environment” and that another child who was at the home was placed in the custody of child protective services.

Authorities said Ferguson and Pena have extensive criminal records. State Police Chief Pete Kassetas detailed Ferguson’s history of drug charges, probation and parole violations as well as shoplifting, child abuse, domestic violence, aggravated battery and kidnapping counts.

Prosecutors said the charges against the three could change depending on what other evidence is unearthed. They also plan to request that the suspects be held without bond pending trial.

District Attorney Marco Serna on Tuesday reiterated earlier statements that his office will use all of its resources to seek justice for the boy.