Willam Blake Marston, 31, died during a parachuting excercise in January last year
An investigation has concluded that a Navy SEAL who died in a parachute training accident in Florida last year became unconscious after exiting the plane.
The investigation also found that Petty Officer 1st Class William Blake Marston was unable to open his main chute, the Virginian-Pilot reported.
It also determined that Marston, 31, shouldn't have been on the plane to begin with because of a discrepancy over whether he was up to date with a required certification.
Officials were unable to determine why Marston was unable to open the main chute during his January 15, 2015 jump in Deland, Florida.
'The most important question is unknowable, despite diligent investigative efforts,' Rear Admiral Brian Losey wrote in his endorsement of the investigation's findings.
According to the investigation, Marston was supposed to open his parachute about five seconds after jumping off the plane, but that didn't happen.
After 15 seconds Marston became unconscious, and he hit the ground after another 15 seconds, breaking his leg as he landed feet first from the 5,000 ft fall.
William Blake Marston during his service, left, and in Stonehill College baseball uniform, right
'Stay with me, buddy! Stay with me!' shouted a security guard who saw Marston fall, according to audio from a 911 call made available by the Virginian-Pilot.
'I need evac now. ... He's not conscious at all,' the witness said.
The investigation also revealed the Marston did not have a current certification that is required to conduct a military free-fall parachute jump.
Marston's certification expired in March 2014. The lapsed certification should have kept him from jumping that day, the investigation determined.
'I concur with the opinion that these areas were not the proximate cause of S01 Marston's death. But, we missed an opportunity to intervene that fateful day by grounding our teammate until these discrepancies were satisfied,' Losey wrote.
Marston lived in Virginia Beach and was a member of SEAL Team 6. He grew up in Concord, New Hampshire and joined the NAVY in 2008.
This 2003 file photo shows United States Navy SEALs during cold-water training in Kodiak, Alaska
Marston was a member of Naval Special Warfare Development Group, better known as SEAL Team 6
ncG1vNJzZmivp6x7pa3IpbCmmZmhe6S7ja6iaKaVrMBwrdGtoJyklWKAdX2Ub29vZ36Ww7p5sn54hWWUnrKlec%2BaqZqbmKrBpnnIp5qinJWjwW7BzZymp6uTnry2v42hq6ak