Jeremiah Oliver, 5, was trying to protect his mother from her boyfriend before killing, prosecutors say

Alberto Sierra Jr. was arraigned in Worcester Superior Court in Worcester, Mass., May 18. Sierra, who is charged with murder in the death of 5-year-old Jeremiah Oliver, whose body was found in a suitcase beside a Massachusetts highway in 2014, pleaded not guilty at his arraignment and was held without bail.Rick Cinclair/Associated Press

Alberto L. Sierra Jr. allegedly killed 5-year-old Jeremiah Oliver, the son of his then-girlfriend, after the boy tried to intervene in a dispute a decade ago between the adults at their Fitchburg home, according to prosecutors.

The child was witness to an argument between his mother, Elsa Oliver, and Sierra that broke out in the kitchen near a closet that Jeremiah was forced “to live in, to sleep in, and to spend his time in” in the home where he lived with two siblings, his mother, and Sierra, prosecutors said in Worcester Superior Court during a hearing last Friday..

After the altercation, the boy emerged “from that kitchen cabinet or closet area and went at” Sierra and “said something to the effect, ‘Don’t hurt my Mommy,’ " Worcester Assistant District Attorney Courtney L. Sans said in court.

In response, Sierra allegedly grabbed the child, lifted him into the air, and slammed his head into the kitchen floor, after which the boy was no longer moving, Sans said.

Sierra has been charged with killing Jeremiah Oliver, who went missing in Fitchburg in September 2013 and whose body was found in a suitcase by the side of a major Central Massachusetts highway in April 2014.

Sierra has pleaded not guilty to a charge of first-degree murder and disinterring a corpse. He was ordered held without bail on Friday.

Sierra was a suspect in the child’s death in 2014, but Sans said it was only because witnesses have come forward in the years since that authorities can connect him not only to the child’s death but also to allegedly moving the child’s body three times before the remains were found alongside Interstate 190 in Sterling on April 18, 2014.

“In the intervening years, there have been witnesses that have come to the Commonwealth’s attention who provided information relative to what transpired in the home leading to the child’s death,’’ Sans said.

After the child’s death, Sierra allegedly placed the body in a bag and “with the assistance of another,” dug a hole, and buried the body, Sans said. But after Jeremiah’s older sister reported being abused to Fitchburg school officials in December 2013, a major search was launched in the region.

Fearing a searcher “would trip over the body,” Sierra allegedly moved it to a second location and then a third before the remains were found in Sterling, Sans said.

According to prosecutors, forensic evidence links Sierra to Oliver’s murder. The child’s body was found inside a bag that investigators allegedly can link to Sierra, who was seen using it to carry tools from his home before the killing, and that other “items” belonging to Sierra were also found in the bag.

Sierra, Sans said, exhibited emotional control over Oliver’s mother.

Sierra pleaded guilty to assaulting Jeremiah’s mother and two of the boy’s siblings, and Elsa Oliver pleaded guilty to endangerment charges relating to other surviving children, according to court documents. Sierra was ordered to serve six to seven years in state prison in 2017 but has since completed that sentence, records show.

During the bail hearing, defense attorney Marissa L. Elkins did not challenge any of the allegations made by prosecutors. But she did argue that Sierra should be given the opportunity to post a cash bail of about $10,000 because even though he knew he remained under investigation for Oliver’s murder, he made no attempt to flee.

Moreover, Elkins said, he suffers from a severe form of arthritis.

But Worcester Superior Court Judge Karin M. Bell concluded Sierra should be jailed pending trial. He faces life without parole if convicted of first-degree murder.

“The court finds that the ‘uniquely severe penalty’ of life without the possibility of parole, the nature and circumstances of this particular case, the Commonwealth’s evidence tying the defendant to the alleged offenses, and the defendant’s history of domestic violence suggest that detention is necessary,” she wrote.

The murder of Oliver caused widespread outrage and led to a major shakeup at the state Department of Children and Families, which was monitoring the family. After an investigation revealed that a social worker had missed eight monthly visits with the boy, that worker and two supervisors were fired. A month later, the DCF commissioner, Olga Roche, resigned.