Even if Troy Buswell admitted drinking heavily before driving into four parked cars the morning he was seen swerving erratically in Subiaco, police still would not have charged him with drink-driving.
The evidence by Police Commissioner Karl O'Callaghan to a parliamentary inquiry into WA Police's handling of the investigation drew incredulity from committee member Tony Buti, who said it undermined the drink-driving message.
It was also revealed that Assistant Commissioner Stephen Bell was forced to approach Department of the Premier and Cabinet director-general Peter Conran for spare keys to Mr Buswell's government car and his gate code because investigating officers could not find the former treasurer.
Mr O'Callaghan told the committee yesterday police were bound by law to prove all elements of an offence when considering what charges to lay.
To support a charge of Mr Buswell driving under the influence after a wedding at Kings Park on February 23, it had to be proved he was incapable of having control of his car, Mr O'Callaghan said.
The officer in charge of the investigation, Det-Sen. Sgt Brian Hunter, said Mr Buswell's car had been so badly damaged by the time it was seen on Roberts Road it could not be proved whether intoxication or mechanical failure was the cause of it swerving.
Mr Buti said there would had to have been at least one crash before the mechanical failure and a triple-0 caller had described Mr Buswell as being unable to stand. "I mean, come on, don't tell me that there's not a strong possibility that this person was under the influence of something," he said.
Mr O'Callaghan said the evidence of the triple-0 caller was in conflict with evidence from other wedding guests - that Mr Buswell had been coherent before leaving the event.
Committee chairwoman Margaret Quirk accused police of second-guessing the courts.
Det-Sen. Sgt Hunter said it would have been easier to investigate the matter if Mr Buswell had agreed to be interviewed, but Mr Buswell's solicitor Laura Willox told police via email on March 13 he did not want to.