AUSTIN—Texas Lt. Gov. David Dewhurst, criticized for failing to disclose details about his vast wealth, is voluntarily cooperating with Travis County prosecutors who want to know whether his public disclosures adhere to Texas ethics law, Dewhurst’s lawyer said.

“We’ve cooperated entirely,” said Dewhurst’s lawyer, famed Austin defense attorney Roy Minton. “We’re just in the process of showing documents to them.”

Travis County Attorney David Escamilla said he is reviewing a formal complaint against Dewhurst by a campaign watchdog group. The complaint followed an Associated Press report about Dewhurst’s personal financial statements, which don’t reveal his riches, estimated to be worth as much as $200 million.

Dewhurst, a Republican, is said to be the richest man in Texas politics, but most of his wealth is contained in a trust whose major assets are not disclosed. As lieutenant governor, he presides over the state Senate and wields tremendous influence over legislation. He is considering a run for higher office as early as 2010.

Escamilla, a Democrat who investigates allegations of misdemeanor offenses by public officials, said he could not discuss any evidence he had received but confirmed he was looking into the matter.

“We’re certainly reviewing the information related to the complaint,” Escamilla said.

Dewhurst spokesman Rich Parsons said Dewhurst had not received a criminal subpoena, but he declined to give any details about his dealings with Escamilla’s office.

“There’s a process to follow and it would be inappropriate to say anything at this time,” Parsons said.

Texans for Public Justice, a liberal watchdog group, called for a probe of Dewhurst earlier this year, alleging that Dewhurst may have violated disclosure laws by allegedly filing incomplete and misleading reports at the Texas Ethics Commission—a Class B Misdemeanor, punishable by a fine of $2,000 and up to 180 days in jail.

TPJ’s complaint followed an AP report examining Dewhurst’s financial disclosure form.

In a statement in September, Dewhurst, 63, said he had followed “the advice of my expert legal counsel in filling out and filing my political financial statement to fully comply with the letter and spirit of the law, and it is a fact I do not know the assets in my trust from which I have received income in excess of $500.”