FORT WORTH (CBSDFW.COM) – The City of Fort Worth has opened up an investigation into the city’s Aviation Department after City Manager David Cooke fired the former director William Welstead.

Cooke is auditing the department and asking Fort Worth Police to open a criminal investigation.

Welstead’s termination happened on September 9, following an internal investigation.

William Welstead (credit: City of Fort Worth)

Cooke said Tuesday the investigations could take several weeks and updates will be provided as findings are made.

“Ethical behavior and accountability are two of our core values here at the City of Fort Worth,” Cooke said in a statement. “We expect all city employees to practice these values, especially our department leaders.”

Roger Venables will serve as the interim director for the Aviation Department.

Venables normally serves as an assistant director for the city’s Property Management Department.

No other details have been released on this matter.

CBS 11 left a phone message for Welstead, but has not heard back so far.