Unless he fully intended to murder her, in which case he'd just tell the press that he was cleaning the hammer and it fell from his hand down onto her head while she was cleaning the floor beneath him or some nonsense. Or maybe he'd just say she had fallen on the knife (hey, it's happened before).
There are two problems with totally unrestricted (ie free) gun ownership: the first is irresponsible owners who do not give the power of the gun the respect it deserves and do idiot things like clean it while loaded, clean it while drunk, play with it while drunk, etc, the second is a corollary of that which is that there's no way to force people to be informed, to even be 'experts' on guns, gun handling, and gun use. If you take away people's excuses to do irresponsible things with it, you take away all doubts that they're somehow inculpable if there's a mishap with it in their hands. That's a sorry comfort for friends/family of victims, but given that there are still victims even when/where guns are illegal I guess that point doesn't really hold as a counterargument does it?
The problem isn't the items used for violence, the problem is violence itself. Our culture glorifies violence, associates violence with power, associates violence with a means of getting what you want when you're otherwise incapable of it, associates violence and domination with machismo and what it means to have strength. There's no dialog about when violence is or isn't appropriate, there's no explication that some kinds of violence are more noble than others, nothing. We have a generation of kids right now who go around wearing Scarface merch, talking about the glory of Tony Montana, all of whom clearly missed the point of the film. Fix that, make clear the line between fantasy and reality, demand consequences for action, demand responsibility, insist on personal accountability, and maybe we'll be closer to stopping violence.
Guns are tools, as they're tools of law enforcement which are made necessary (to at least match the force of criminals, if not overpower it) by the violence in the society being policed. Firearms are the tools of hunters, some people in the world still hunt for their food or at least to supplement what diet they already have. The 'tools build, not destroy' argument simply can't hold water. You'd be forced to concede that knives were tools by your own argument, and yet people misuse them for violence. Is it that hard to believe the same is true of firearms?
The Sun is a big steaming pile of a magazine, let's make no mistake about that, but tell me it isn't a sensational overreaction to ban knives when it's treating a symptom of a much larger and more insidious problem.