The bodies of five U.S. Marines killed in an air crash in Pakistan returned to U.S. soil Sunday.

Military investigators continued to search the crash site in the rugged mountain area of southwest Pakistan for the last of the seven victims and clues to what caused the crash of the military refueling plane Wednesday.

"The search will continue," said Lt. Col. Martin Compton of the U.S. Central Command. "The Marines will leave no one behind."

The plane carrying the remains of five Marines killed in the plane crash arrived shortly before midnight Sunday at Dover Air Force Base in Delaware after a flight from the U.S. Rhein-Main Air Base in Germany.

The names of the Marines found were not released. Central Command officials said there were expecting the remains of six Marines to be on the flight, but authorities at Dover said there were only five coffins.

The base chaplain, Lt. Col. Jim Barlow, led a short prayer before the flag-draped coffins were taken to the base mortuary. It was not clear when the bodies would be flown to their final destination. All were based at Marine Corps Air Station Miramar in San Diego

In Wednesday's crash, the seven were killed when their Marine KC-130 fuel tanker slammed into a mountainside and exploded while approaching an air base Americans have been using at Shamsi in southwestern Pakistan. Although U.S. forces in Pakistan have occasionally faced gunfire and other hostile actions, Defense Department officials say they have no evidence hostile fire brought down the plane.

Military officials also have said they have no indication that bad weather caused the crash, which caused an explosion that was seen and heard in a Pakistani town 20 miles away.

The Associated Press contributed to this report.