NEW ORLEANS – The manslaughter charges brought against two relatively low-ranking BP rig workers in the deadly Gulf of Mexico disaster may be as far as federal prosecutors are willing to go. Or maybe they intend to use the two men to work their way up the corporate ladder.

The Justice Department has said only that its criminal investigation is still going on. As a result, others are left guessing about prosecutors’ intentions.

“Either there simply isn’t evidence that anybody higher up was involved, or the department has concluded the only way it’s going to make its case against more senior corporate officers is if it charges and eventually obtains cooperation” from the two men, said David Uhlmann, a University of Michigan law professor and former chief of the Justice Department’s environmental crimes section.