Major General Michael DeLong, Marines Corp deputy commander in the Atlantic, told a news conference at the US airbase in Aviano, north-east Italy, that "air-crew error" had caused the plane to shear cable-car wires and send the car plunging into a mountain.
Gen DeLong's report said the crew of the EA-6B Prowler surveillance aircraft "aggressively manoeuvred their aircraft, exceeded the maximum air speed and flew well below 1,000 feet" on a training mission on 3 February.
Lieutenant-General Peter Pace, commander of US Marine forces in the Atlantic, said he had ordered a pre-trial investigation into the crew and an investigation of all other officers involved in the mission in the Dolomites mountains.
The crew inquiry would consider "whether charges such as involuntary manslaughter or negligent homicide, damage to private and government property and dereliction of duty should be referred to a general court martial," he said.
Italian prosecutors are also investigating the incident in which the victims, crushed below the mangled wreckage of the car in the resort of Cavalese, died instantly.
Gen DeLong said Marine Corps investigators had not been able to question the "mishap crew" members . The men had declined to answer questions. "We have not been able to interview the air crew so we have no idea what they thought or what they were thinking." he said.