Former treasurer Troy Buswell could still be charged with drink-driving over the crash that ended his ministerial career.
As Colin Barnett accused the Opposition of "distasteful" questions in State Parliament over the affair, Labor called for an independent inquiry "so the public can have confidence criminality is not being covered up".
Opposition Leader Mark McGowan said he found it "inconceivable" the Premier's chief of staff Brian Pontifex and senior adviser Narelle Cant did not ask Mr Buswell's chief of staff Rachael Turnseck what preceded his breakdown when they met for 45 minutes on February 25.
"If she was at the wedding and she advised Mr Barnett's most senior advisers of that, what did they ask her about those events," Mr McGowan said.
"I find it inconceivable that they would not have asked what happened on that night."
On Monday in the immediate wake of the revelations of Mr Buswell's accident on February 23, Police Commissioner Karl O'Callaghan said it would be hard to prove a drink-driving charge without a breath test.
Yesterday, a spokeswoman for Mr O'Callaghan said while he stood by that statement, it was based on detail available at that time. "Further information has come to light and the matter is under investigation by major crash specialists," she said.
Those officers would assess the evidence and decide whether there should be a charge.
In Parliament, Mr McGowan asked the Premier why he told reporters last Saturday he was confident Mr Buswell would soon return to work.
"I knew he was out of hospital," Mr Barnett said. "I knew he was improving. My guesstimate, In my view, at that stage, he would be back in two weeks.
"What do you expect me to do? Ring his mother? Ring his sister? Ring his doctor? For goodness sake. The guy's had a breakdown, he's in a serious situation and I respected that. And I do today."
After more questions and interjections, the Premier said: "I have never experienced such distasteful inquiries about a member of this House."