James William Gallant has pleaded guilty to second-degree murder in the death of Lavinia Campbell. (CBC)

One of two teenagers charged with murdering an elderly Dartmouth woman in December has pleaded guilty to second-degree murder and been sentenced to life in prison.

Jamie William Gallant, 18, was originally charged with first-degree murder in the death of Lavinia Campbell, whose body was found beaten in her Jackson Road home.

On Wednesday, the Crown and defence announced a plea bargain and Gallant pleaded guilty to the lesser charge.

The teenager was also sentenced to life in prison with no chance of parole for 17 years, starting Dec. 19, 2011. He is also required to submit a DNA sample.

"He's simply eligible for parole in 17 years. It doesn't mean he'll get it and he could end up spending the rest of his life in jail," said Crown prosecutor Terri Lipton.

Campbell's body was found on Dec. 16.

The 79-year-old was a widow known for taking in stray cats.

The court heard how Gallant and another teenager went to Campbell's house to steal cigarettes, money and car keys.

The court was told Gallant thought he heard Campbell wake up. He went into her bedroom, hit her on the head with a flashlight and then kneed and kicked her in the face

She was found dead on the floor next to her bed two days later.

"I'm really sorry for the things I've done," Gallant said in Nova Scotia Supreme Court on Wednesday.

He said he does not understand why he beat Campbell to death.

"I can't turn back the clock," said Gallant. "So I'll try at least to fix the future."

Campbell's granddaughter Caroline Derksen travelled from Vancouver, B.C., to read a victim impact statement on Wednesday.

"I think that it brings some closure for my family," she said.

"There's some comfort in knowing he can't do this to anyone else's grandmother and my heart really goes out to his family because this can't be easy for them to deal with either."

A 16-year-old Dartmouth boy, who was also charged with first-degree murder in her death, pleaded guilty to manslaughter last week. His identity is protected by the Youth Criminal Justice Act.