The boy is listed in critical condition at Oregon Health & Science University in Portland, according to police.
Abo is charged with two counts each of first-degree assault and first-degree criminal mischief. The assault charge is a Class A felony and Measure 11 offense, punishable on conviction by a mandatory minimum prison sentence. The criminal mistreatment charge is a Class C felony.
He is lodged in the Washington County Jail in Hillsboro on $1 million bail. Given Abo's local law enforcement connections, he was moved to Washington County from the local facility. He tentatively will be arraigned at 1:20 p.m. Monday in Yamhill County Circuit Court.
Yamhill County Sheriff Jack Crabtree also requested that McMinnville police investigate the alleged abuse.
Crabtree confirmed that Abo was terminated as a deputy with his department.
"His job performance was not up to our standards," Crabtree said. "We tried working with him."
McMinnville police reported Abo was a reserve with the Yamhill department at the time of his arrest.
Police gave this account of the incident:
The sheriff's office responded Tuesday night to a medical call at Abo's residence, 420 N.E. Evans St.. The boy was transported by Life Flight helicopter to OHSU
An Oregon State Police SWAT unit and the U.S. Marshals assisted in taking Abo into custody Saturday.
News-Register records show Abo was awarded a Yamhill County Sheriff's Lifesaving Award in April 2012.
Anyone with information about the case is asked to call McMinnville Police Detective Hugo Cerda at 503-434-7307.