I wouldn't imagine that in this case anything the young man said would be of any importance to the prosecution.

Obviously a shot to the neck could have come from a botched suicide attempt. But there'd have been a lot of bullets flying around, and it'd be premature to assume that without more evidence that the trajectory of the bullet could have been consistent with that.
........
As for the gun licence business, it's surely irrelevant to the issue of gun law reform. After all, if it turned out they did have the guns legally, that could equally be argued as evidence that gun registration restrictions don't work.