Burton Hagar, center, speaks to attorney Verne Paradie, right, following a bail hearing on Friday. Justice Thomas Warren granted bail or $10,000 cash or $100,000 surety to Hagar, who is accused of murder in the 1979 death of his infant son in Brunswick.

PORTLAND, Maine — The Maine Supreme Judicial Court on Tuesday denied an appeal by a Brunswick man convicted of killing his infant son in 1979.

Attorneys for Burton “Ben” Hagar, now 64, of Farmington argued in the appeal that the state’s “corpus delecti” law, which states that a confession alone is not enough evidence to convict someone, and that prosecutors must provide other evidence of a crime, should be amended to mirror the federal law, which requires the court to also weigh the credibility of the additional evidence and find that it is reliable.

Hagar was arrested April 7, 2017, following his indictment on murder charges by a Cumberland County grand jury. He initially pleaded not guilty.

Hagar was charged in connection with the death of his 4-month-old son, Nathan Hagar, who was found unresponsive in the family’s Brunswick apartment and died at the former Parkview Hospital on May 9, 1979.

Nathan Hagar was originally believed to have died as a result of Sudden Infant Death Syndrome, or SIDS, but detectives reopened the case quietly in 1991, state police said at the time of the arrest.

During an April 10, 2018, hearing, Nathan Hagar’s mother, Venus Nappi, testified that she did not recall an interview with then-Brunswick police officer Mark Phillips the day of her son’s death during which she told him that Nathan had been vomiting and had diarrhea that day. She said she did not recall a pediatrician telling her Nathan might have at least one digestive system condition, chalasia or pyloric stenosis.

Phillips testified that day that he found a pillow in the crib with white or light-yellow mucus on it, but he acknowledged to Verne Paradie, Burton Hagar’s defense attorney, that since a 2014 interview about the case, he may have remembered additional details. He also told Paradie that he was not completely sure the baby was not breathing when he found him in the crib.

In July 2018, Justice Thomas D. Warren ruled that the infant’s death was a homicide after police said new evidence determined he was likely smothered with a pillow.

Hagar had repeatedly admitted to causing his son’s death — admissions that Paradie has characterized as unreliable — but the case could not move forward until a court determined a crime had been committed.

Under the terms of a conditional plea agreement, Hagar pleaded guilty to manslaughter in exchange for a 15-year sentence.

But the plea agreement was reached only on the condition that the attorneys who lost the case would appeal to the law court in order to obtain more clarity in such cases because “oftentimes, the only witness to the case is the deceased party,” Paradie said.

Paradie argued in the appeal that the state should adopt the federal corpus delecti standard, and said Phillips’ testimony was “suspect at best and is also not itself reliable enough to establish trustworthiness of the inconsistent statements of Mr. Hagar.”

“In this case, there is absolutely no substantial independent evidence to establish the trustworthiness of Mr. Hagar’s statements over the years and to establish his guilt beyond a reasonable doubt,” Paradie wrote.

A written decision issued Tuesday by the law court declined to adopt the federal standard of corpus delecti.

The decision stated, in part, “It is not for us to weigh the credibility of a witness,” adding that the trial court’s factual findings are supported by competent evidence “and are sufficient to establish probable cause to believe” that someone killed the baby.

“It’s obviously disappointing,” Paradie said Wednesday afternoon by phone. “We would have liked to go to trial on the case, but he was given a favorable offer of manslaughter and 15 years. If we had gone to trial and lost, he could have been convicted of murder and gone to jail for 25 years, and he would never have gotten out.”

Calls to the office of the Maine attorney general were not immediately returned Wednesday.