HOUSTON -- The Harris County District Attorney has started a criminal investigation into the Houston Police Officers' Union financial issues, first exposed by KPRC Local 2 Investigates last month.

Police union board members confirmed that union secretary Ronnie Martin has been suspended from his union job as part of the investigation. He was recently voted out of office, so he would have been departing at year's end, regardless.

District Attorney Chuck Rosenthal acknowledged opening the criminal inquiry, saying paperwork from the union's finances would be examined.

Martin told KPRC he did nothing wrong when he sold a union-owned car to his son. Prior to that, another vehicle was sold to a wrecker-driver with ties to Martin's family. Martin said the sales were handled just like past sales of union cars.

Another union officer, treasurer Jeff Larson, was fired after the KPRC Local 2 Investigates report last month because $10,600 from the sale of that car to Martin's son could not be accounted for.

Union president Hans Marticiuc said the treasurer could not provide an adequate explanation, but when union leaders started asking more questions about the money, the $10,600 in cash suddenly turned up in a union hall safe.

Sources involved in this investigation told Local 2 Investigates that the purchase price of the vehicles will be examined.

Some union members said they tried to bid higher than the $10,600 purchase price but their bids were not considered at a union auction. They claim the union should have received more money for the sale.

The HPOU executive board held an emergency meeting last week about the new questions, but no formal action was taken.

Rosenthal said he did not yet know when a grand jury might consider criminal charges in the case.