Could be.
There is also an, as yet, unsubstantiated rumour that one of those killed was the guy's brother, which may point to the family dispute being more likely.
A family dispute over a Will is one suggestion.
An impending run in with the taxman is another.
Neither really seems enough to set the whole thing off, though.
Fuck knows.
There will be an investigation, then an inquiry, then they will probably make some changes to the gun laws, if he had acquired the arms legally.
If he had got them illegally, there isn't much that can be done.