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San Ramon police officer Louis Lombardi arrived in Department 20 courtroom in Martinez, Calif. to be arraigned on multiple counts in relation the CNET scandal Friday May 6, 2011. (Karl Mondon/Staff)

Federal investigators have questioned a San Ramon officer caught in a corruption probe that surfaced with the sale of confiscated drugs and has widened to include allegations of false arrests and prostitution, according to several sources with knowledge of the development.

It is unclear why the FBI got in touch this weekend with 38-year-old Louis Lombardi, who is on administrative leave from the San Ramon Police Department after being arrested May 4 on five felony charges that he sold drugs to confidential informants and took cash, drugs and guns from police seizures.

An FBI spokeswoman said she would not have immediate comment on her agency's involvement in an investigation that so far has been conducted in tandem by the state Department of Justice and Contra Costa District Attorney's Office. Dirk Manoukian, Lombardi's attorney, would neither confirm nor deny reports that the FBI contacted his client.

The development follows a federal judge's decision last week to re-evaluate her ruling on a civil suit over the 2008 slaying of a 29-year-old Antioch man in a police drug raid after initially rejecting it this past January.

Timothy Wayne Mitchell was shot by a Pittsburg detective working with the Central Contra Costa Narcotics Enforcement Team, or CNET, of which Lombardi was a member and also part of the raid that ended in Mitchell's death.

It was later learned they were deceived by a suspect who had stolen Mitchell's identity, but police said that he reached for an officer's weapon in a struggle.

Federal Judge Susan Illston's new ruling cited the allegations against Lombardi and former CNET commander Norman Wielsch, who also faces numerous charges. Oakland-based attorney John Burris represents Mitchell's family.

"We always had suspicions about the Mitchell case. It never made sense," Burris said.

Burris cautiously welcomed the involvement of federal investigators -- and a less entwined perspective -- in the Contra Costa corruption probe.

"It's not surprising to me there would be federal involvement here. With all this widespread misconduct, it's like a conspiracy," he said.

Lombardi is free after posting $500,000 bail May 6.

His arrest was part of an ongoing investigation that surfaced with the February arrests of Wielsch and Christopher Butler, a former Concord-based private investigator. The two are accused of numerous felony counts that they conspired to sell drugs confiscated in police raids.

Prosecutors say Lombardi stole money from at least three seizures and in 2007 solicited a confidential informant to steal money from a building where Lombardi had conducted a legal search. Prosecutors have asked to keep secret the identity of informants they say Lombardi threatened.

Since his drug arrest, Butler has also been charged with conspiring with former Danville Officer Stephen Tanabe to set up men for DUI arrests to tarnish their standing in divorce and child custody hearings. Tanabe has also been charged with drug and bribery offenses.

Butler, 49, Wielsch, 50, and Tanabe, 47, are free on bail and have pleaded not guilty.

Robert Salonga covers public safety. Contact him at 925-943-8013. Follow him at Twitter.com/robertsalonga.