A Chicago Police sergeant has been indefinitely relieved of police powers after shooting an autistic 18-year-old in the arm during an off-duty confrontation early Sunday in Morgan Park.

Officers involved in shootings are automatically put on desk duty for 30 days under CPD policy, but the Independent Police Review Authority recommended that the sergeant be taken off the streets for the duration of their investigation — a process that can take months or years.

Supt. Eddie Johnson agreed with their recommendation, according to CPD spokesman Anthony Guglielmi.

About 5 a.m., the 5th District sergeant was off-duty and driving home in his personal vehicle when he saw an 18-year-old man “acting suspiciously” near the intersection of Wood Street and Hermosa Avenue on the Far South Side, Johnson said at a Sunday press conference.

The 18-year-old, who has autism and suffers from schizophrenia, had been reported missing a few hours earlier by his foster mother, Guglielmi said on Monday.

The sergeant tried to question the 18-year-old, but he was “elusive and unresponsive,” Johnson said. The encounter then “escalated in some way,” prompting the sergeant to shoot him in the arm, he said. He was treated and later released from Christ Medical Center in Oak Lawn.

A police statement initially said the two got into an “armed confrontation.” Johnson said no weapon was recovered from the 18-year-old.

The sergeant is now assigned to paid desk duty.

“We still have many unanswered questions,” Johnson said.