A new investigation into the disappearance of Malaysia Airlines Flight 370, which vanished off the coast of Vietnam a year ago this weekend, has found that all members of the crew were behaving normally before the incident, the Associated Press reports.

Some theories concerning the disappearance of MH370 have focussed on the possibility of the plane's pilot or co-pilot committing suicide; however, this report found no evidence to support that interpretation. According to the AP, the report found that the plane's captain, Zaharie Ahmad Shah, had no known history of apathy, anxiety, or irritability.

Neither Zaharie nor his co-pilot, Fariq Abdul Hamid, showed signs of "social isolation," drug or alcohol abuse, or other behavioral changes, The New York Times reports. Footage from airport closed-circuit television cameras did not reveal changes in either man's mannerisms.

The investigation also found that the battery for the data recorder's locator beacon had expired more than a year before the plane's disappearance. According to the AP, the instrument should still have recorded all flight information before the aircraft's presumed crash, despite the fact that the battery had expired.

The significance of this, according to The New York Times, is that the beacon might not have sent out signals for the full 30 days for which it was designed. The cockpit voice recorder's beacon, however, had been replaced, the Times reports. It would have expired in June of 2014.

The BBC reports that some relatives of passengers lost on the plane are dissatisfied with the investigation. Sarah Bajc, who lost her partner Philip Wood, described the report as "nonsensical ass-shielding." Another, unnamed relative described it as "useless."

The full report can be read here.

[Photo credit: AP Images]