Damning footage of race horses being shocked with Tasers is expected to form part of a police case against Melbourne Cup-winning trainer Darren Weir.

The 48-year-old was one of three people arrested during Wednesday raids on properties – including stables – at Ballarat and Warrnambool, where police seized four Taser-like devices, known as “jiggers” in the racing industry.

One of the trio – a 26-year-old – was released pending further investigation, Victoria Police Assistant Commissioner Neil Paterson said, adding that the complex investigation stretched back to August last year and involved allegations of corruption in sport.

“I have heard that there may be footage in the public arena … of jiggers being used,” Mr Paterson said, appealing for people with information to come forward.

Weir, 48, and a 38-year-old Yangery man, believed to be one of the trainer's foremen Jarred McLean, remain in custody.

Mr Paterson said an unregistered firearm and three jiggers were seized from one property during the raids, and a fourth device and suspected quantity of cocaine at a second.

“It may well be that all people today who are interviewed will be released without charge,” he added.

“This is a complex investigation making an assessment of many aspects of evidence and I anticipate that assessment will take some time before we can make decisions in context of charges.”

In an earlier statement police detailed the areas of criminality being investigated, which included obtaining financial advantage by deception, engaging in conduct that corrupts a betting outcome and use of corrupt conduct information for betting purposes.

Racing Victoria boss Giles Thompson refused to identify the parties involved, other than to confirm each is a licensed participant in the state's racing industry.

“Racing Victoria's primary objective is to protect the integrity of the sport … and ensure a level playing field for all,” he said.

Racing Victoria alerted Victoria Police after launching investigations into parties last year.

Weir is Australia's most prolific and successful trainer and trained the 2015 Melbourne Cup winner Prince of Penzance, ridden to victory by Michelle Payne who famously became the first woman to win the coveted trophy.

Five Weir-trained horses raced at Mornington on Wednesday, with seven due to start at Pakenham and Werribee on Thursday, and nine at Moonee Valley on Friday.

There has been no news of suspensions following Wednesday's arrests.

Victorian Racing Minister Martin Pakula said the investigation showed authorities were enforcing rules “without fear or favour”.

“As minister for racing and a racing lover, I'm committed to maintaining the integrity of our sport and any allegations of breaches are extremely disappointing,” he said in a statement.

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