Prosecutors in the Los Angeles suburb of Riverside County — home to the biggest wiretapping operation in the United States — likely broke the law when they approved as many as 738 wiretaps without proper approval, according to an investigation from USA Today and The Desert Sun, citing interviews and court records.

The wiretaps, according to an earlier report from USA Today, intercepted calls involving thousands of people, leading to more than 300 arrests, usually at the request of Drug Enforcement Administration agents. But the surveillance rested on shaky legal turf, and Justice Department officials reportedly declined to bring the evidence into federal court, for fear that it wouldn't withstand legal scrutiny.

As the investigation today found, federal law requires that the district attorney personally sign off on wiretap requests, but in this case, a former Riverside County attorney reportedly did not do so, instead handing the wiretaps to other lawyers. The investigation cites a court decision from a neighboring county that determined a sign-off from a deputy prosecutor did not meet the bar, but the Riverside County district attorney reportedly kept delegating the responsibility.

"I didn't have time to review all of those," the former district attorney reportedly said, according to the investigation published in USA Today. "No way."