The forensic report on Martin's clothing says "contact" shot. Contact with the clothing, that is. The clothing will obtain some of the burn energy, etc. and make the wound on the body appear as one that (had it been to bare skin) came from farther away.
I'd say the evidence has the muzzle of the gun no more than 3 inches from Martin's skin.
Isn't it obvious? There was a struggle for the gun and it went off accidentally.