UPDATE: Internal affairs unit officers have charged a 29-year-old constable with disclosing information about the arrest of former West Coast Eagles player Ben Cousins.

Cousins was arrested on March 11 following an alleged low-speed police chase through Bicton and Mosman Park.

The officer from the south metropolitan district has been charged with four counts of disclosing official secrets, to a Channel 7 reporter.

The offences are alleged to have occurred between March 11 and 17.

Acting Commissioner Steve Brown told 6PR that alarm bells rang when there was only one journalist waiting outside Fremantle Police Station at about 2am after Cousins' arrest.

An investigation uncovered a "personal relationship" between the accused officer and the journalist.

It was revealed this week that hundreds of WA Police officers could be hit with criminal charges if it was found they unlawfully accessed information from the police computer system about Cousins and Daniel Kerr.

Mr Brown said about half of the police who accessed information about the men would have accessed the information through “professional curiosity” because they were in neighbouring areas,

The remainder did not appear to have any specific reason to access the files.

He said the journalist has not done anything wrong.

The 29-year-old officer has been stood down from all duties and will appear before Perth Magistrate’s Court on May 5.

The WA Police Union today released a press statement announcing the union would provide legal assistance to the officer charged with disclosing official secrets.

President George Tilbury said WAPU would fund legal assistance up to, and including, the officer's first court appearance next month.

"The board will then reassess legal assistance after being briefed by our legal team," he said.