Dallas city officials are authorizing an independent investigation into the deletion of millions of Dallas police evidence files. City Council on Wednesday approved a nearly $550,000 contract to hire the law firm that employs Erin Nealy Cox, the former top federal prosecutor in North Texas. A city IT employee was fired after deleting the massive loads of data files while moving them to another server. The city manager and police chief knew about the data loss in April, but the council didn't find out until the D-A told defense attorneys in August. Cox says her team's probe will take three-months.