Republican senators who are convinced Sound Transit leaders played fast and loose with facts about the agency’s light rail expansion plans got a chance last week to prosecute their argument in a court of public opinion.

Thursday, the senators will make their case that some of the same operatives played fast and loose with the law while abetting the campaign to get Sound Transit 3 passed by voters.

This legislative inquest is being conducted by the state Senate Law and Justice Committee.

It comes at the behest of GOP Sens. Steve O’Ban and Dino Rossi who insist lawmakers, then voters, got duped on the magnitude of this latest Sound Transit undertaking to fulfill its manifest destiny.

Last week’s hearing in Kent centered on the content and intent of Senate Bill 5987. It passed in 2015, giving Sound Transit authority for this year’s new and higher taxes — including a hike in car tab fees — to finance the expansion.

O’Ban, an attorney, contends the wording of the bill obfuscated Sound Transit’s intention to use a 1990s-era depreciation schedule that overvalues vehicles to calculate the excise tax levy rather than a newer one which more accurately traces a vehicle’s declining value. It’s part of why car tab fees surged this year, surprising, and in some cases shocking, vehicle owners.

He also argued that Sound Transit misled lawmakers on what they actually wanted to collect from those living in the taxing district that covers parts of King, Pierce and Snohomish counties. Agency officials said the “full” amount was always represented as $15 billion — not the $28 billion it is now. As far as the $54 billion, which is the sum total of all expenses, no one ever heard that figure, he said.

O’Ban unsuccessfully pressed a Sound Transit lawyer and two high-ranked employees to confess they’d left out a few details in all their presentations and documents. They didn’t. The $15 billion was for 15 years and it grew to $28 billion for 25 years based on added demands of communities to be served. Voters were told $54 billion is what ultimately will be spent.

Republican senators didn’t buy the explanation. They felt deceived and the purpose of the hearings is to hold someone accountable.

Last week’s hearing didn’t include testimony of those allegedly caught up by this purported con job — lawmakers.

Leaders of the House and Senate transportation committees, who negotiated the final version of the bill, didn’t get summoned to recount what they knew and when they knew it.

Nor did Sen. Doug Ericksen, who could have explained why he drafted Amendment 53 to Senate Bill 5987. It would have got rid of the old vehicle valuation schedule and put in place a newer one of his crafting. Then O’Ban or others in his caucus could have testified on why the Senate turned it down.

What could have emerged is a clearer picture of lawmakers’ reliance on outside forces to help them craft and pass complicated and controversial legislation.

And how when such bills get passed in Olympia without all lawmakers understanding the full ramifications, they can feel conned and compelled to investigate.

Contact political reporter Jerry Cornfield at 360-352-8623; jcornfield@heraldnet.com or on Twitter: @dospueblos.