Mayor Danene Sorace of Lancaster, Pennsylvania, responded on Thursday, June 28, to a viral video showing a Lancaster police officer tasing an unarmed black man sitting on a curb from behind.

“I was upset by it and it is a great concern to me,” Sorace said, adding an investigation was launched into the incident.

The footage of the incident shows a black man sitting on a curb, he appears to be following the officer’s commands to straighten his legs before the officer deploys a taser to the man’s back. Credit: City of Lancaster via Storyful