Pittsburgh (CNN) Protesters angry over the death of an unarmed teen who was shot by police this week marched Friday for the third straight night down the streets of downtown Pittsburgh.

Four people were arrested as hundreds of demonstrators blocked streets, Allegheny County Police Superintendent Coleman McDonough said.

Police are looking for a black sedan that drove through the crowd late Friday, said Chris Togneri, the city spokesman. No injuries were reported, he said.

Protesters were near PNC Park, where fans were leaving a Pittsburgh Pirates baseball game, when the car drove through, CNN affiliate KDKA reported

'How do you justify that?'

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