MADISON, Wis. (AP) -- The state's lead criminal investigator has resigned, telling staffers it's been "very difficult" serving under Attorney General J.B. Van Hollen.

James Warren has led the justice department's Division of Criminal Investigation for more than 10 years. He's earned the confidence of law enforcement officers across the state.

The division provides support to local law enforcement and investigates a wide range of cases, including drug trafficking and Internet crimes against children.

Wisconsin Sheriffs and Deputy Sheriffs Association director Jim Cardinal says local law enforcement and district attorneys have a great deal of respect for Warren and his resignation is a big loss.

Warren was hired by Governor Doyle, when he was the attorney general. He also worked for Peg Lautenschlager, also a Democrat, before Republican J.B. Van Hollen took office in January.

(Copyright 2007 by The Associated Press. All Rights Reserved.)