The mother of a Milwaukee man who died after gasping for breath in a police car says justice has been denied because the officers won't face federal charges.

Sonya Moore spoke to reporters Tuesday after the U.S. Department of Justice announced it was closing its investigation surrounding the 2011 death of 22-year-old Derek Williams. She tearfully said her son didn't deserve to die in police custody as officers ignored his pleas for help.

She says she's hurt and won't be able to sleep.

U.S. Attorney Jim Santelle says he didn't charge the officers because he would have had to prove they intended to break the law. He says negligence, mistakes and poor judgment aren't sufficient to establish a federal criminal-rights violation.

Moore's attorney says a lawsuit is possible.