There is CLEARLY not enough info provided to determine what actually occured, much less if it was an ND or a gun malfunction.

One round could have done the damage to all three. Or it could have went full auto and dumped a full mag... The article doesn't say how many rounds were fired. It also doesn't say if the gun discharged while in the hands of the owner, another, or sitting on the bench. Even a gun as crappy as a Jennings, I would find it hard to believe it self-discharged just sitting there. It's possible, but the highly unlikely.

Only a full recreation based on the evidence and witness statements will determine what happened. I've done a few shooting recreations. They are way too much fun (seriously). I know it a bad situation, but doing the recreations are just a blast.

I've investigated a couple of shootings where the person claimed spontaneous firing from the gun. It was disproved every time. The first was an M-16. I did some seriously dangerous things to try to get the gun to fire without touching the trigger in a controlled setting. Nada. The next one was a Siaga AK-47 in an attempted homicide. I inspected the gun and then informed the forensic scientist on the case that there was not fricken way. It was new, clean and stock.
The only time I've ever seen a gun AD without a booger picker on the boom lever was a Winchester 70 rifle with a post 64 trigger that had some home gunsmith hack job done to it. With the saftey on, you could slam the butt stock on something and get the sear to slip. This was an accidental death case that seriously looked like a homicide. Those triggers were always iffy anyway. That's why they stopped using them. Well, they sucked too...

Anyway, I'm babbling now...