BATON ROUGE, La. - Louisiana State Police disciplined four state troopers over a side trip they took to the Grand Canyon and Las Vegas in a state-owned SUV on their way to a conference in San Diego.

Investigative reports by WWL-TV and the New Orleans Advocate first prompted the administrative investigation. The side trip cost taxpayers at least $30,000 in added expenses and improperly-billed overtime.

Former commander of State Police, Col. Mike Edmonson announced his retirement in the wake of the investigation.

"One incident does not define us," said current-Superintendent Col. Kevin Reeves, "We will inevitably make mistakes, but together, our goal must be to promote an environment that is not only conducive to public service and cultivates professional development and growth but also maintains public confidence in our agency."

The agency's then-head of internal affairs, Major Derrell Williams, was one of the troopers on the side trip. He was overtime-ineligible, but billed the state for 'K-time' for the weekend hours he was at the conference.

Monday, current Superintendent Col. Kevin Reeves announced Williams would be demoted a second rank to Lieutenant.

The agency announced the four troopers' discipline over the trip after an 8-month administrative investigation into the 2016 trip. rThe demotions take effect immediately and come with hefty pay cuts.

Lt. Rodney Hyatt was demoted to sergeant. Master Trooper Thurman Miller received a letter of reprimand and State Police said Trooper Alexandr Nezgodinsky was "counseled".

In February, the four troopers were asked to reimburse the state for their hotel stays and compensation for their time in Las Vegas. State Police did not say whether they were asked to reimburse the state for their time at the Grand Canyon.

"This administrative investigation as an unfortunate but necessary process. As a department charged with the public safety of our citizens, we must hold ourselves accountable before we can begin to hold others accountable," Reeves said in a statement released late Monday.

At the time, Metropolitan Crime Commission President Rafael Goyeneche called for a prosecutor to review the administrative findings to determine if any laws had been broken.

"This goes beyond the pale of simple mistakes. I will be interested to see how the state police handles the investigation," Goyeneche said in February.

The statement released Monday about the agency's administrative findings only said the La. State Police Commission, an oversight board embroiled in turmoil of its own, would review the cases.

The four officers have the right to appeal.

Governor John Bel Edwards announced after the controversy over the trip that the Division of Administration and the Louisiana Legislative Auditor would conduct a sweeping audit of all state police travel. The results of that probe have not yet been released.