The Justice Department has dropped the manslaughter charges against two BP rig supervisors over the 2010 Deepwater Horizon rig explosion in the Gulf of Mexico, which killed 11 workers and caused the worst offshore oil spill in U.S. history. In total, four former BP employees faced criminal charges after the disaster. Two of the cases have already been resolved without the employees serving prison time. On Wednesday, prosecutors dropped the involuntary manslaughter charges against the other two employees, Donald Vidrine and Robert Kaluza.