A woman was charged with killing her 8-year-old son by keeping him locked in the trunk of a car while she was at work. Her lawyer says the boy was not restrained.

Devin Gibson was found dead Sunday. His mother, Michelle Joyce Gibson, 36, was charged Monday with second-degree murder, voluntary manslaughter and two counts of felony child abuse, authorities said. She was jailed in lieu of $100,000 bail.

A preliminary autopsy showed Devin died of hyperthermia. High temperatures during the weekend in nearby Asheville were in the 70s.

Gibson left her son in the car's passenger compartment, not the trunk, while she worked, said her appointed lawyer, Rangy Seago. He said the back seat in Gibson's car folds down to allow access to the trunk from inside.

Gibson worked as a certified nursing assistant at Mountain Trace Nursing Center (search) in Jackson County. Seago said she left her post occasionally to check on her son.

"He was never restrained in the trunk away from the passenger area," Seago said. "I don't think he died being locked in the trunk. He could get out. All this trunk stuff is sensationalism. It's a sufficiently horrible tragedy as it is."

However, Jackson County Sheriff Jimmy Ashe said there is evidence that the boy was locked in the trunk. The last time anyone other than Gibson saw the boy alive was Friday night, the sheriff said.

After putting in a 17-hour day Saturday, Gibson returned to work at 7 a.m. Sunday, and about 4 p.m. told a co-worker she believed her son was dead, Ashe said. She returned to her apartment in Asheville, about 40 miles away, he said.

Asheville police found Gibson in the back seat of the car at the apartment complex, holding her dead son.

Gibson faces up to about 17 years in prison if convicted.

"She cries almost all the time," Seago said. "She's very grieved over the loss of her son. Here's a poor lady who's lost her child, and on top of that they come back and charge her with murder."

Police Gibson and Devin had been in and out of homeless shelters until a couple of months ago, when they moved in with friends.