These are the kinds of confrontations between MacDonald and the alleged intruders that seem likely to me:
1. The intruders and MacDonald engage in a desperate violent fight crashing into furniture and walls, resulting in upturned and broken furniture with the items that had been on the furniture strewn about the room. There might have been items used as make shift clubs or defense against knife attacks.
If a knife was used by the attackers one would expect to see slashing type wounds and stabbing wounds with widened holes created as MacDonald moved about. If the attackers were experienced knife fighters at least some of the knife wounds would have probably suggested that the attacker held the knife with the blade up. If the attackers gained the upper hand in such a fight and had attempted to incapacitate MacDonald one would have expected lethal or near lethal wounds when they cut or choked MacDonald in a way that they would have been sure he couldn't recover and attack them.
2. The attackers gain the upper hand immediately by grabbing and holding him. An attack on a single individual, even a green beret trained soldier, by multiple strong individuals might have subdued MacDonald before MacDonald could put up much of a defense. If this happened there might have been injuries to MacDonald where he was grabbed and held. And after MacDonald was subdued once again one would have expected lethal or near lethal wounds as they cut or choke MacDonald in a way that would guarantee he couldn't recover and attack them.
3. The attackers gain the upper hand immediately by knocking MacDonald out with a club or other method. Once again one would have expected lethal or near lethal wounds as they cut or choke MacDonald in a way that would guarantee he couldn't recover and attack them.
MacDonald didn't have wounds consistent with any of these kinds of confrontations. From my perspective, this kind of argument falls short of definitive proof that MacDonald was guilty, but it is evidence that strongly suggests that he is. You [Henri McPhee] seem to disagree. Could you describe a confrontation between MacDonald and the intruders where the expected or plausible outcome is that he sustains the kind of wounds that he had?