iStock/Thinkstock(NEW YORK) — A Florida teenager accused of killing his mother over an argument about his school grade has been charged as an adult with first-degree murder.

A Volusia grand jury indicted Gregory Ramos, 15, this week on one count of first degree murder — a crime that could be punishable by a life sentence, according to Spencer S. Hathaway, a spokesman for Florida’s State Attorney’s office.

The grand jury charge appeared to catch the state attorney's office off guard.

“I’m surprised, I’m shocked, I’m bewildered by the fact we’re in a position to have to prosecute a 15-year-old for murdering his mother,” State Attorney R.J. Larizza said of the decisions in the statement.

“That’s a sad day, and it’s a sad announcement I’m making, and I take no pleasure in the fact that the state attorney’s office will be prosecuting the 15-year-old for the murder of his mother as an adult.”

Ramos' attorney did not immediately respond to a request for comment on Friday from ABC News.

Ramos confessed to killing of his mother, Gail Cleavenger, 46, according to Volusia County Sheriff Mike Chitwood.

Ramos later led the police to the body of his mother which he buried in a fire pit at a church, Chitwood said.

Ramos allegedly strangled his mother to death on Nov. 2 after the two had an argument about his D grade while his stepfather was on a business trip in Seattle, Washington.

In previous press conferences, Chitwood has said that during police interrogations, Ramos seemed proud of himself.

“He believed he was the smartest person in the room and he continued to tell us his theories of what he believed and why: what happened to his mom and where we should be focusing our attention,” Chitwood said earlier this month.

Eventually, officials said, the teen changed course, admitted to the murder, and walked investigators through his plot and its execution.

“She was a mom," Chitwood said of Cleavenger earlier this month. "She was a wife. She was a sister. By all accounts she was an amazing human being.”

After Cleavenger’s killing, Ramos allegedly got two friends to come and help him stage a fake burglary at his home. Ramos and both co-defendants — Dylan Ceglarek, 17, and Brian Porras, 17 — remain confined at the Volusia County jail, according to Hathaway.

Porras' attorney did not immediately respond to a request for comment on Friday from ABC News. It was not immediately clear who is representing Ceglarek.

“The co-defendants were charged by information with being accessories after the fact of a first degree murder,” Hathaway told ABC News. He went on saying that the two could be sentenced to 30 years in prison if found guilty.

The trio are set to be arraigned in December and they have not yet entered a plea.

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