Cranston's city council may be launching their own investigation into problems within the city police department.  Council President John Lanni Jr. says they are considering whether to invoke special investigative powers to dig deeper than a recent State Police report.  Issues of concern include whether police conducted unjustified surveillance, and how much Mayor Allan Fung knew about problems in the department.  Fung answered questions from the council for over three hours Tuesday, but some members are unsatisfied with his answers and want more details.