The cost of prosecuting Bradley Robert Edwards — the man accused of being the Claremont serial killer — is about to top $3 million, even though he has yet to enter a plea to allegations he murdered three women.

Mr Edwards, who has been in custody for almost 18 months, is due in court again in July, accused of murdering Sarah Spiers, 18, Jane Rimmer, 23, and Ciara Glennon, 27. They disappeared between January 1996 and March 1997.

WA Police formed the Macro task force with the aim of finding the man responsible for the murders that have haunted WA for more than 20 years.

The West Australian can now reveal that after setting aside $1.5 million in last year’s State Budget for the massive case, Treasurer Ben Wyatt has included another $1.8 million for the anticipated costs of the proceedings in the coming year.

That will take the cost to more than $3.3 million — with what is likely to be a complicated, long and highly scrutinised trial still possibly to come.

The Budget papers noted that the prosecution “has the potential to be one of the longest and most complex criminal cases ever conducted in Western Australia”.

It is already the longest running and most expensive murder investigation in Australian history.

In a court hearing in March, lawyer Genevieve Cleary, who is representing Mr Edwards, revealed the size of the document pile connected to the case “would strike fear into the heart of any lawyer”.

Prosecutors said they were still trawling through more than 1.5 million pages of evidence, which are being categorised and digitised, to be then placed on a spreadsheet for ease of use.

“It’s extraordinarily different to other cases,” Ms Cleary said.

She has indicated that if Mr Edwards faces any trial, it is unlikely to be until at least the second half of next year.

Including the high-profile, complicated prosecutions in the past year, the Budget papers say that as at February 28, the Office of the Director of Public Prosecutions had prosecuted 375 trials and expected about 170 more by the end of the financial year — a year-on-year increase of 12 per cent.

As at March, the DPP office had prosecuted 49 trials in the Children’s Court in 2017-18 and expected a similar number in 2018-19. The DPP reported an overall conviction rate of 93 per cent, with a conviction rate of 73 per cent after trial in the District and Supreme courts in 2017-18.