Johnathan Fair was indicted by a grand jury Wednesday on four counts of first-degree murder

Illinois prosecutors say they will seek a natural life sentence for a teenager accused of fatally beating a 4-year-old after she spilled juice on his Xbox.

Johnathan Fair, 19, and the child's mother told hospital workers in December that the girl, Skyler Mendez, had a head injury from a fall, Waukegan police said. Skyler died at Lurie Children's Hospital in Chicago within 48 hours of the alleged fall after she had surgery to treat swelling in her brain, according to state prosecutors.

But the severity of the child's injuries prompted an investigation, and police determined that the girl had been physically abused, according a police statement. The girl's mother was not at the home, located about 40 miles north of Chicago, when the incident occurred.

Fair - whom police identified as the boyfriend of the child's mother - was indicted by a grand jury Wednesday on four counts of first-degree murder, the Lake County State's Attorney's Office said. He was originally charged with aggravated battery to a child, police said.

The young man admitted to investigators that the child hadn't actually fallen, Assistant State's Attorney Steve Scheller told The Washington Post on Monday. Instead, Fair acknowledged that he was with Skyler on Dec. 13 when the toddler spilled juice on an Xbox console and played with the stove, and he responded by severely shaking and striking her, Scheller said.

Fair also said he kicked Skyler down a hallway in the home, Scheller said. The attack rendered the girl unconscious. Scheller said the state will seek natural life in prison for Fair, which grants no possibility of parole, because of the "brutal and heinous" nature of the alleged beating.

Doctors also found bruising on the girl's body and injuries to her brain, which may be indicative of older incidents of abuse, Scheller said.

"It's a sad case," he added.

Fair's attorney, Sam Amirante, did not immediately return a phone call requesting comment Monday - but he told the Associated Press on Sunday that his client deserves the presumption of innocence. He did not comment on the allegation that the girl's death was sparked by the spilled juice.

"When the real facts come out, he will be acquitted," Amirante told the AP.

A GoFundMe set up in the girl's name by her relatives originally said that Skyler had suffered a tragic accident.

In an update, however, the organizers wrote that they had learned "a monster" had killed their niece.

"We just found out that this was no tragic accident. Our sweet angels life was taken from us by a heartless human being," Cecilia Villalpando wrote. "Just adding more pain into our lives knowing that someone took our babygirl. We greatly appreciate your donations and support."

Fair's arraignment will take place Feb. 17.