CONCORD, N.H. (AP) – A man accused of killing his girlfriend’s 5-week infant 23 years ago was convicted of manslaughter Wednesday but cleared of second-degree murder.

George Knickerbocker, 46, will spend between 15 to 30 years in prison rather than a possible life term had he been convicted of murder.

He was charged with killing Adam Robbins in February 1983. He was not arrested until December 2002 and was indicted in February 2003.

Knickerbocker, who went by the name Nicky Robbins at the time, had been living with the child’s mother.

The victim’s mother, Denise Dow, wept and embraced family members as the verdict was read. “Justice is finally being served,” she said. She sat through the trial with a photograph of her infant son on her lap. “I’ve waited a long time, and I see this as a big victory,” she said.

In the Merrimack County Superior Court jury trial, defense lawyers described the mother as a party girl involved in drinking and drugs, and suggested she could have inflicted the fatal injuries.

But prosecutors said that shortly after he was arrested in 2002, Knickerbocker told his sister that he had “lost it” with Adam and had shaken the baby the day he died.

The baby was rushed to the hospital with a fractured skull and bruises on his head, chest and ankles. He died soon after.

The case was returned to Merrimack County after the state Supreme Court ruled last year authorities did not violate Knickerbocker’s rights in trying to prosecute him for murdering the infant 20 years after the death.

In 2004, Merrimack County Superior Court Judge Edward Fitzgerald had ruled prosecutors had given no compelling reason for the 20 years between the crime and the indictment.

At first, Knickerbocker and the boy’s mother were suspects, but police could not accumulate enough evidence to charge either one. The investigation stopped in 1983, but the boy’s mother asked the attorney general’s office to reopen the case in 1996.