The Justice Department...is expected to seek to join civil lawsuits stemming from the Gulf of Mexico oil spill, the first major federal legal action in the disaster...By joining the private litigation, Justice Department lawyers are positioning themselves to play a major role in the coming litigation, including depositions of key witnesses...That could aid the government's continuing probe into the disaster aimed at building a civil and possibly a criminal case against the companies involved...A steady trickle of plaintiffs in the civil suit have dropped their cases and turned to the [claims] fund in recent weeks and numbers are expected to increase as the case slowly works its way through the court process. [refers to BP, Transocean]