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A South Shore man who opened fire with an assault rifle on a CTA Blue Line train at the Lasalle Street platform, striking a train car five times, offered no motive for the shooting, prosecutors said Friday.

Lorenzo Jones, 25, carried a Hi-Point .45 caliber rifle onto the platform at 11:21 a.m. Thursday, said Assistant State’s Attorney Erin Antonietti.

He then opened fire with the carbine, striking the first car of the train, she said. At least five rounds were fired, but no one was injured.

Antonietti said Jones had been convicted of a misdemeanor count of selling items on CTA property, but when Cook County Circuit Judge Donald Panarese Jr. asked her about Jones’ motive, she said he did not give one.

Jones was charged with one count of aggravated assault/discharge of a firearm, one count of possession of a stolen firearm and two counts of aggravated unlawful use of a weapon and ordered held on $2 million bail.

The conductor operating the train heard five to six popping sounds and at first thought the train was malfunctioning until he saw Jones standing on the platform with a rifle, Antonietti said.

A bystander who saw Jones holding the rifle with two hands ran up an escalator and called 911, she said.

Jones was arrested after Chicago police officers responding to a flash message saw Jones walking along Polk Street, according to Antonietti.

The conductor and the witness identified Jones as the gunman, she said.

The rifle was recovered and found to be stolen from Indiana, Antonietti said.

Jones admitted to detectives that he had opened fire with the weapon, she said.