Japanese investigators concluded Thursday that 20 people, including four American employees of Boeing Co. were criminally negligent in the 1985 crash of a Japan Airlines Boeing 747 that killed 520 people.

The Gunma Prefectural Police recommended that the 20 officials of Boeing, Japan Airlines and the Ministry of Transportation be tried for professional negligence causing death. The recommendation was sent to the public prosecutor, who will decide whether to issue indictments.The airliner departed Tokyo for Osaka, Japan on Aug. 12 but pilots soon lost control of the craft due to a break in the rear pressure bulkhead and crashed in the mountains northwest of Tokyo, killing 520 passengers and crew members.

An investigation revealed the plane had been improperly repaired by Boeing after the plane's tail scraped a runway during a landing in 1978.