(05-25) 13:05 PDT DANVILLE -- A former Danville police officer pleaded not guilty Friday to new charges that he committed wire fraud when he allegedly exchanged text messages with a private investigator to coordinate drunken-driving arrests later dubbed "dirty DUIs."

Stephen Tanabe, 48, appeared in federal court in Oakland, where prosecutors added charges to existing counts of fraud, conspiracy, and extortion under color of official right.

Prosecutors say Tanabe worked with Christopher Butler, 50, a private eye hired by women allegedly seeking to have their husbands set up for drunken-driving arrests. The men were usually in divorce or child custody battles, prosecutors said.

In May, Butler pleaded guilty to seven federal criminal counts and said he had paid Tanabe with cocaine and a handgun to make three arrests on his behalf.

In the new indictment, prosecutors said Butler and Tanabe had exchanged text messages to coordinate two arrests and had discussed Tanabe's compensation in a third.

Prosecutors said Butler's phone showed that minutes before the Jan. 9, 2011, arrest of a man outside a Danville bar, the private eye texted Tanabe, "They are up + heading for the door."

Tanabe's attorney, Tim Pori, said prosecutors were using an obscure law usually applied to politicians who use the telephone to accept bribes. According to the indictment, the server for Butler's phone is located in Kansas and the allegedly illegal communications with Tanabe crossed state lines, making the exchange a federal crime.

"This kind of prosecution is esoteric and this is not the way the statute is normally used," Pori said.

Tanabe resigned last year from the Contra Costa County Sheriff's Office, which employed him as a Danville officer. The charges against him carry a maximum 20-year prison sentence and $250,000 fine.