Californian prosecutors are expected to drop criminal charges against a private investigator involved in the HP boardroom spying scandal.

Bryan Wagner, a data broker hired by the IT giant last year to probe the source of a news leak, pleaded guilty to charges of identity theft and conspiracy in a federal court earlier this month.

However, deputy attorney general Robert Morgester, said yesterday that his office would not oppose a defence motion to dismiss all state charges against Wagner.

Under Californian law, the state is prohibited from prosecuting someone for a crime if that person has already admitted to the same acts in a federal case.

The attorney general's office is expected to review the Colorado resident's federal charges and plea agreement over the next few days, to confirm that he admitted to the same crimes, before making a final decision, Morgester said.

The HP scandal began in 2005 when the company's board become suspicious of private information being leaked to journalists. Wagner was hired by the company in an attempt to determine which boardroom member was passing on the information to the media.

The 29-year-old admitted that he was part of a conspiracy that used "fraud and deceit" to gain social security numbers and other confidential information, to allegedly obtain the private telephone records of an HP director, several reporters and their family members.

Former HP chairman Patricia Dunn and three other people were also charged in the criminal investigation on various counts, including conspiracy and identity fraud.

The case continues.