The government is investigating reports of illegal trading by all but one of Mexico's 25 stock brokerage houses in connection with the 1987 market crash, an official was quoted as saying Friday.

Roberto Hoyo D'Addona, the country's fiscal attorney general, was quoted as saying his department has received 50 complaints of alleged stockbroker fraud stemming from the crash.Investigations in five of those complaints turned up no evidence of wrongdoing, he was quoted as saying by Mexico City newspapers.

He said investigations by the Department of Treasury were being carried out "without regard to the political or economic power of those involved."

"There exist accusations against all of the brokerage firms except one. The Treasury Department is only investigating if the National Securities Law has been violated in order to tell the (attorney general) whether or not crimes exist to prosecute," D'Addona said.

He did not identify possible securities violations but said the investigations were related to the October 1987 crash, when Mexico's market index plunged by 74 percent in 28 trading days.