NASHVILLE (AP) - The United States Attorney for Middle Tennessee is stepping down to enter securities fraud law in Nashville.

Jerry Martin made his mark combatting white-collar crime, including health care fraud, during his three years as the government's top lawyer in the region.

Martin told The Tennessean (http://tnne.ws/16rNhGH) his departure Monday might seem abrupt, but he wanted to wait until he handled the effects of automatic federal budget cuts on his office.

Martin will create a Nashville office for Robbins Geller Rudman & Dowd. The San Diego-based firm represents investors who sue with claims of deception and fraud.

"I wouldn't be happy representing big corporate interests," Martin said Wednesday. "I'm more interested in unearthing fraud and representing the underdog."

Martin's tenure was marked by several large awards, involving tens of millions of dollars, although an appellate court recently reversed $94 million in awards his office won against health care companies.

"Jerry put the office on the map," said Nashville civil rights attorney David Garrison. "Jerry's legacy will be tied to taking on causes that are tough and sometimes controversial."

Among cases that drew substantial attention was one that involved the opening of a mosque in Murfreesboro. Martin argued that Rutherford County officials created a "mosque standard" for public notices by presenting bureaucratic obstacles.

Martin recalled something the late Jim Neal once told him. Neal held the U.S. attorney office for less than a year and a half in the late 1960s, during which time he sent Teamsters president Jimmy Hoffa to prison.

"He said one of the things you should know is when best to leave," Martin said. "You never want to stay too long."