TWO positive swabs were taken from horses at last Saturday's Menangle meeting as police investigate trainers' alleged inside knowledge of swabbing procedures, Harness Racing NSW says.

It capped one of the worst weeks in the sport's history, beginning with the chief steward Bill Cable's car being firebombed last Friday.

This incident, still under police investigation, is not thought to be related to the swabbing scandal.

Trainer Darryl Thomas has been informed by stewards that the pre-race blood samples taken from Points North and Zoro on Saturday were found to have elevated TCO2 readings above the threshold of 37mm/mol per litre. Both horses have been stood down and Thomas will face stewards at a later date.

Two stewards, Matthew Bentley and Paul O'Toole, resigned on Monday after being informed of allegations that they had not taken pre- and post-race swabs from certain horses in certain races.

Harness Racing NSW has since asked people of interest to supply phone records as the investigation widens and the Firearms and Organised Crime Squad formally became involved on Thursday.

The investigation could lead to criminal charges. Harness Racing licensees found guilty of being involved face suspension or disqualification and the possibility of being warned off racecourses around the world.

Harness Racing NSW has been asked by police not to make any more public statements in relation to the case after earlier in the week telling the Herald it would name people who had received letters. The governing body has instructed anyone with information about the investigation to contact Crime Stoppers.