Morley Liberal MP Ian Britza skipped a high-level meeting with the New York Police Department to go to his wife's home State of Texas while on tour with a parliamentary committee he quit weeks later.
It was the third time since being elected in 2008 that Mr Britza has gone to Texas on the WA taxpayer.
Speaker Michael Sutherland is investigating Mr Britza going absent during the community development and justice standing committee's $120,000 trip last month to Britain and the US to research seniors and police policy.
Mr Britza and fellow Liberal Chris Hatton quit the Labor-dominated committee this week after Police Commissioner Karl O'Callaghan and the Premier claimed its June report into Troy Buswell's traffic crashes was biased.
But the move has prompted questions over why the pair went overseas with the committee last month if they no longer wanted to be on it.
Committee chairwoman Margaret Quirk yesterday confirmed Mr Britza, who was deputy chairman, missed a scheduled meeting with NYPD deputy commissioner Dermot Shea on July 11.
"He didn't even tell me, he just nicked off," she said. "When I went down to the hotel foyer and said, 'Where's Ian', the research staff said he's gone to Dallas a day early."
The delegation was in Dallas for a conference on the ageing between July 12 and 16.
Ms Quirk said Mr Britza had been keen for the committee to attend the conference but also left that event midway through the last day to visit an in-law in nearby Fort Worth before staying on in the US.
Mr Britza's two other research trips to Texas, costing taxpayers $12,000, were during the festive seasons of 2008-09 and 2011-12.
Mr Britza told Channel 7 that committee research officers had told him the NYPD meeting had been cancelled and gave him permission to leave early, a claim Ms Quirk disputed.
He defended his three Texas trips on taxpayers.
"I don't care if it was six times," he said. "It's the only in-law I have. My family matter to me more than what you matter."