VOLUSIA COUNTY, Fla. — The 15-year-old Florida boy accused of killing his mother after an argument over a bad grade will be prosecuted as an adult, the State Attorney’s Office said Thursday.

A grand jury indicted Gregory Ramos of DeBary on Thursday for first-degree premeditated murder in the slaying of his mother, Gail Cleavenger, 46, earlier this month. Ramos has also been charged with tampering with a crime scene and abuse of a dead body.

He will be transferred to an adult court, where he will be tried, State Attorney R.J. Larizza said during a news conference.

Investigators said the boy confessed to strangling his mother after they got into a fight over a "D" he received in a class. He then allegedly buried his mother's body beneath a fire pit at River City Church in DeBary.

They said he then called two friends to help hide her body and stage a robbery at his home. The two friends, both 17 years old, are also in custody and have been charged with accessory after the fact on a capital felony, Larizza said.

"This is a shocking case. I've been in the criminal justice system since 1980... and I'm surprised, I'm shocked, I'm bewildered by the fact that we're in a position to have to prosecute a 15-year-old for murdering his mother," Larizza said.

Sheriff Mike Chitwood agreed with the state attorney's decision.

"I don't think we're talking about a typical 15-year-old kid here," he said.

Larizza said that because Ramos is younger than 18, he won't face the death penalty.

In an appearance before a judge Friday, Ramos and one of the 17-year-olds was ordered held without bond. The other 17-year-old friend was granted $100,000 bond and bonded out but was ordered to wear a tracking device. All three are scheduled for an arraignment December 6.