French military investigators say loose papers left in an F-16 that crashed at a Spanish airbase could have sent the fighter jet into its deadly spiral.

A report released this week concludes a multinational investigation into what happened before the Greek plane's failed takeoff and crash in Albacete, Spain, on Jan. 26. The French military report found that papers left in the cabin, perhaps a checklist, likely shuffled shortly before takeoff, causing an "accidental modification" of the position of rudder controls that stabilize vertical motion.

Both pilots and nine French servicemen on the ground died, and 21 people on the ground were injured, in what NATO called the worst crash during a NATO exercise in recent memory. The report emphasized that no country or individual could be held responsible.