The attorney for a Brooklyn postal worker who was wrongly arrested while innocently delivering mail on St. Patrick’s Day wants an investigation into the cops who harassed his client — saying he’s “curious” about the contents of a cup a lieutenant can be seen clutching in a video of the arrest.

After filing a notice of claim on behalf of letter carrier Glen Grays at Brooklyn Supreme Court Monday, Kenneth Ramseur seemed to imply the supervising officer may have been enjoying a little St. Paddy’s cheer.

But “I cannot say there was alcohol in that cup definitively,” he said.