I also think that this is a strong case of genetics at play considering that the shooter didn't even spend time with his bank robber father. The psychopath apple didn't fall far from the psychopath tree.
However, we should be cautious about making statements about genetics. Apart from there not being any major scientific research behind it, it also leads to disturbing effects like the state detaining blood relatives of someone that commits crime because they will be more at risk of committing crimes in the future, thought-crimes, etc.
Do we know this? Do we know what his motivation was?
He's not just a random crazy person that bought a gun and went on a spree, there was a lot of planning involved, so he's probably a terrorist of some sort.
Wow doesn't that fit nicely into some narrative. His phrenologic profile was off the charts too and a Virgo on top of that!
There's more where that came from.
No new gun control laws came out of Sandy Hook, or any of the other mass shootings in this decade. Why should this one be any different?
On the other hand the majority of NATO training emphasises rapid single shots, with bursts only for initiating ambush or breaking contact ( and usually only when authorised by the NCO ). Being limited to single-shot isn't therefore too much of a restriction.
Additionally, fathers and sons share more than just genetics. They quite often share upbringing and culture. Not to mention the Father set that example of bank robbing.
Looks like a bump stock was used though https://apnews.com/e74a33083fb84b1b94c1ce3da986fd4f