A detective inspector accused of gross misconduct by abusing his rank to "gratify himself sexually" with junior female colleagues was obsessed about the colour of their underwear, a disciplinary hearing was told.
Simon Hurwood, who at one time worked in Cleveland Police's professional standards department, resigned from the force last month and is not represented or attending the hearing at Middlesbrough FC.
The officer, who joined the force in 1991, faces allegations relating to 21 female colleagues, some of whom were civilian employees but most of whom were officers.
He denies their allegations and his responses to the complaints will be read out at the ongoing hearing.
John Beggs QC, for the chief constable, said: "Their common theme is that of DI Hurwood, over a lengthy period of time, abusing his rank and status to gratify himself sexually with almost always subordinate and vulnerable females."
The hearing was told he relentlessly pursued women, often while on duty, on police premises, abusing his position and lacking integrity.
He would quickly get hold of their personal mobile phone numbers, target women with issues in their private life and offload his own troubles to gain sympathy, Mr Beggs said.
Mr Hurwood would then send ordinary texts before sending flirtatious ones, and seek to get explicit photos or videos from the women, the barrister said.
Mr Beggs said one of his "several obsessions" was to seek to identify what colour knickers they were wearing.
The hearing continues.