This young man was very likely a US military Veteran - either a Marine or a Sailor who had been wounded in the VietNam War. He appears to be quite young. Although the file write-up states his age between 20 and 30, I think it is likely in his early 20's.
The healed bullet wound might indicate that he had been in a Naval Hospital, perhaps Bethesda, Portsmouth, or Balboa Naval Hospitals, as those were the main ones. I wonder if x-rays were taken of the wound? If a bone had been broken, perhaps it could be compared with x-rays taken of wounded servicemen who were treated at one of the above hospitals.
His haircut is within 1968 regulations for the Navy, but a bit long for Marine Corps standards. He may have been recently discharged and on his way home when he was murdered.
The Navy Pea Coat could indicate that he was a Navy man, although it is also possible that he was a Marine who purchased the coat at a Navy exchange or uniform shop - or that he was borrowing the coat from a friend for the cold weather trip he was on. Marines do not and did not wear Pea Coats as part of their uniform.
The USMC tattoo means either that he was a Marine or possibly that he was a Navy Medical Corpsman who had served with the Marines in combat. US Navy Corpsmen are the "medics" for the Marine Corps.
If he was still on active duty when he died, he would be carried on the books today as a "deserter", since he was never identified. If he had been discharged, the Navy or Marine Corps would not have been looking for him. Either way, his records should be on file at the St. Louis Military Personnel Records Center.
Only Officers had their fingerprints on file in 1968. Enlisted men might be fingerprinted for work in high security jobs, but those fingerprint cards would not necessarily be in their military personnel records.
The 4 inch deep puncture wound that killed him could have come from an icepick or screwdriver. It could also have come from a Marlin Spike. That is a round pointed spike used by sailors to work ropes and untie knots. Often a Marlinspike is attatched to a sailor's folder knife, and they are usually 3 to 4 inches in length, and about a quarter inch in diameter.
It is also possible that he was killed with a "shiv" made from a sharpened nail. These are often found in prisons and carried by convicts.
A spike type bayonet could also have been the weapon, as could a sharpened pencil.
I wonder if this young man might have been traveling home for the Thanksgiving holiday. He was dressed nicely and well groomed. Could he have been hitch hiking? Perhaps he was driving and picked up a hitch hiker.
He never made it home.