CHICAGO (CBS) — Someone shot out a window on a small Pace paratransit bus late Wednesday night, as it was driving on the Eisenhower Expressway.

Pace spokesman Rocky Donohue said the minibus is used to provide door-to-door service for people with certified disabilities.

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Three or four passengers were on the bus around 11 p.m. Wednesday, as it was headed east on the Eisenhower near the Independence Boulevard exit, when someone fired a BB pellet that shattered a window, according to Pace and Illinois State Police.

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One passenger was injured by flying glass, and taken to a hospital for treatment, but was not seriously hurt.

Police said no one was in custody Thursday morning.

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Pace was conducting its own investigation, and talking to the driver and passengers about the incident.