A family demanding justice for a police killing in 2012 sees hope in their case.

The mother of Mohamed Bah met with investigators from the U.S. attorney’s office and says she’s optimistic about potential federal criminal charges against the officers involved.

Hawa Bah says she shared her witness account of what happened the night her son was gunned down by police back in September of 2012.

She says she called 911 to get an ambulance for her mentally ll son, but says the police instead showed up and shot him during a confrontation.

NYPD officials refute the claim and say officers tried to subdue him with a taser and rubber bullets first. They say they opened fire on Bah only after he came after them with a knife.

But Bah's mother says her son was the target of racial discrimination.

"I talk to them, 'Please, my son never do nothing wrong. I just called an ambulance to take him to the hospital. Let me talk to him. There's a protocol.' They refused and killed my son, Hawa Bah said. "I hope this will stop."

Bah says she had been trying to meet with former U.S. Attorney Preet Bharara for years before securing a meeting with his interim replacement.