According to court documents, Anthony Waiters struck the teenager with a baseball bat during the nearly 18 months the boy was allegedly held captive.
Waiters, 29, was arraigned Thursday in San Joaquin County Superior Court and was being held in jail in lieu of $1.9 million bail. Jail officials said late Thursday they did not know whether he had an attorney, and police have declined comment, citing a judge's gag order.
Waiters faces felony charges including aggravated mayhem, false imprisonment and child endangerment. Michael Schumacher, 34, his wife, Kelly Layne Lau, 30, and the boy's one-time guardian, Caren Ramirez, 43, face similar charges.
The boy escaped the couple's home in Tracy last week, jumped over a backyard fence and sought help at a nearby gym. He was found nearly naked, emaciated and with a chain around his bloodied ankle.
Waiters' mother, Alice Waiters, said Wednesday that her son did not abuse the teen.
Waiters was arrested Tuesday at his job in Pleasanton, where he is a call center representative for the Bay East Association of Realtors, according to the association.
All four suspects have not yet entered pleas and are due back in court Jan. 5.
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