BP’s stock plummeted and took much of the market down with it on Tuesday, as the US federal government announced criminal and civil investigations into the Gulf of Mexico oil spill.

BP engineers, meanwhile, were mounting a renewed effort to stop the gusher, with a method which will initially make the leak worse.

Attorney General Eric Holder, who was visiting the Gulf to survey the fragile coastline and meet with state and federal prosecutors, would not say who might be targeted in the investigations into the largest oil spill in US history.

“If we find evidence of illegal behavior, we will be extremely forceful in our response,” Holder said in New Orleans.

BP’s stock nose-dived on Tuesday, losing nearly 15 percent of its value on the first trading day since the previous best option, the so-called “top kill”, failed and was aborted at the government’s direction.

It dipped steeply with Holder’s late-afternoon announcement, which also sent other energy stocks tumbling, ultimately causing the Dow Jones industrial average to tumble 112 points.