It was an inside job. Local and federal authorities broke up an identity theft ring made up of Saks Fifth Avenue employees who allegedly stole customer information and used that to buy $400,000 worth of designer bags and shoes that were resold on the black market. Operating out of Saks’ flagship midtown store, accused ringleader Tamara Williams filched the info of some 50 customers and then distributed that to four sales associates, the Manhattan District Attorney’s office said Monday.