He had attempted his gun purchase before this altercation, so I think the altercation was not the beginning of what he was up to.
I don’t understand why the police don’t report more of what they know around this, given that the one suspect is dead.
Maybe the police had a report of the altercation and they didn't follow up on it.
Just one of many possibilities.
Your running under the assumption that there is only one involved in this.
The police however operate on the “till we are 100% sure it was one person we’re not talking” assumption.