That's a good question. That's the best estimate we have. Some of those are from police homicide data having to do with incidents in which there were two or more people killed. Whether those were prosecuted would obviously depend on whether there was an offender who was alive.
My guess is that in almost all those instances.... In fact, if you look at the data, I think you'll see that in all but one of the instances the person was identified, in large part because so many of them are incidents in which people know each other.