The mother of a 4-year-old boy who died under suspicious circumstances four years ago has been charged with his murder.

Alexis Dixon, 31, was taken into custody late Monday evening and is being held on $2 million bail on charges of murder and assault on a child younger than 8 years old resulting in death. She's scheduled to be arraigned Wednesday.

Court records also list her name as Alexis Barrow. She declined an interview request from jail.

Dixon is charged in the April 24, 2010, death of Mark Allen Dixon, who died at Children's Hospital Central California in Madera after being found injured the day before in the family's travel trailer in the 22000 block of Stockdale Highway. The location is west of Bakersfield.

Deputies said at the time that Mark suffered from suspicious injuries and possible head trauma. The boy's injuries were not consistent with explanations that had been given as to how he had been injured.

There were "dozens and dozens" of scars on his body, deputies have said.

Dixon told investigators she'd been lying down when she heard a thud come from another room, according to a search warrant deputies filed in court. She said Mark hit his head after falling from a 2-foot tall table.

The search warrant said Dixon told investigators she placed the boy by a wall outside the trailer, but he slid down and hit his head on a pole, causing further injury.

In an April 2011 interview with The Californian, Alexis Dixon said her son used to bang his head on objects on purpose and pick at his skin, creating sores. But court documents say the boy was examined by a doctor three days before his death and no injuries were noticed.

Dixon was the only person around when Mark suffered his injuries, the documents say.

Detectives continued to investigate for four years and in March 2014, the case was submitted to the Kern County District Attorney's office for review, according to a sheriff's department news release sent out Tuesday. On March 24, the DA's office issued a warrant for Dixon's arrest.

Part of the reason for the delay is that a pathologist needed to determine what injuries were inadvertently caused by medical staff in an effort to save the child, including operations to his head.