One of the country's most senior police officers is to be interviewed under criminal caution over claims that he leaked internal emails containing personal data.
Avon and Somerset chief constable Nick Gargan will be questioned by watchdog the Independent Police Complaints Commission (IPCC) over allegations that he breached the Data Protection Act.
The claims were unearthed during an investigation into allegations that he abused his position by making "inappropriate advances" to younger female members of staff.
Mr Gargan, who has been suspended since May, has pledged to co-operate with the inquiry and said he wants to return to work as soon as possible.
IPCC deputy chair Rachel Cerfontyne said: "As part of our investigation, the IPCC has uncovered evidence that the chief constable may have breached the Data Protection Act by sending emails concerning police business, some of which contained personal data, to individuals unconnected to the force.
"On July 8 I formally brought this matter to the attention of the police and crime commissioner for Avon and Somerset who referred Mr Gargan's conduct to the IPCC the following day. Mr Gargan has now been served with a notice informing him that this aspect of his conduct is subject to a criminal investigation."
So far the IPCC has interviewed more than 50 members of staff from the force and sifted through computer and telephone data.
A spokesman for the Chief Police Officers Staff Association said: "Chief Constable Gargan is pleased that progress has been made in relation to the allegation concerning inappropriate behaviour and that this allegation is no longer being treated as a criminal matter.
"Chief Constable Gargan shall continue to co-operate with the investigation. He is keen to return to work and hopes that the investigation can be progressed expediently."
IPCC investigators are continuing to analyse the material they have gathered and are finalising arrangements to interview Mr Gargan in the coming weeks over allegations of gross misconduct as well as the criminal claims.
Avon and Somerset Police and Crime Commissioner Sue Mountstevens said: "The Independent Police Complaints Commission (IPCC) has made me aware of new evidence in their ongoing investigation into the conduct of the Chief Constable.
"I have referred the matter to the IPCC to investigate and the chief constable remains suspended."