The Chicago Police Department launched an investigation into how officers responded to violence that broke out late Saturday during a large gathering of young people in the city’s downtown tourism district.

The investigation comes after a viral video showed a mob attacking a couple as they exited a Loop store and it follows allegations of police inaction.

As the attack unfolded, police failed to respond to calls for help and even drove past, said Lenora Dennis, who witnessed the beating and helped the couple get to safety.

“It makes me feel scared. It terrifies me that people are either asleep at the wheel or that they’re willfully blind,” Dennis told the Tribune on Wednesday.