Probable Cause Report States "Reason For Occurrence Undetermined"

Undetermined. That's the Probable Cause ruling from the National Transportation Safety Board regarding a suspicious July 2004 controlled-flight-into-terrain crash of a Piper Navajo in the eastern Adirondacks of upstate New York.

As Aero-News reported, pilot Milton Marshall and passenger Michael Keilty were killed when the twin-engine aircraft flew into a heavily wooded area near Ticonderoga, NY under clear skies. In the days following the July 10, 2004 accident, it came to light Keilty was under FBI investigation for allegedly defrauding senior citizens -- and he had attempted to take out a life insurance policy on himself the day before the crash.

The Connecticut Post reports investigators also found the magazine from a .380-caliber pistol at the impact site, with two rounds missing. The actual gun was not recovered... and the report states no weapon of that type could be linked to either Keilty or Marshall.

Further casting suspicion on the circumstances of the crash is a $4,000 loan Keilty had extended to Marshall. The pilot was reportedly providing flight instruction to Keilty in exchange for paying back the loan.

Investigators state the Navajo (file photo of type, below) climbed 600 feet over rising terrain in the final 48 seconds of radar coverage, with no apparent erratic deviations from course. The aircraft struck a strand of old-growth trees jutting above younger trees, according to the NTSB.

Marshall was a retired airline pilot with 32,000 flight hours, according to the Board. Keilty had reportedly told Marshall and others he was also a pilot, although the NTSB found that to not be the case. In the days leading up to the accident, people close to Keilty told NTSB investigators the man's demeanor had changed, and his personal hygiene apparently deteriorated.

Marshall's daughter has maintained the crash was not an accident, according to the Post. Kathy Leonzi said in a 2005 interview her father was  "very safety conscious and meticulous about his flying," adding he "would never crash into trees."

The NTSB notes at Marshall's last medical exam in 2002, his heart exhibited "severe calcific atherosclerotic coronary disease with 90 percent narrowing of the left anterior descending coronary artery and 75 percent narrowing of the right coronary artery." The Board adds there was "no evidence of significant chronic myocardial ischemic change, no coronary artery thromboses and no evidence of a recent or old myocardial infarction," however, and family members said Marshall appeared to be in excellent health.

A definitive cause of death could not be determined for either Marshall or Keilty, due to the condition of their remains, according to the NTSB.

FMI: Read The Full NTSB Probable Cause Report