Any known reason(s) for the Massacre at the supermarket in Boulder?

The shooter had mental health problems.

It is way too easy for people with mental illness to get their hands on firearms. Enacting programs to proactively prevent firearms from being sold to dangerous people is not a violation of anyone's 2A rights. If you believe otherwise then you don't understand 2A. Additionally if you need another adult to explain to you how a gun differs from a knife or a car, then you need to take a course in logic, because you don't understand that either.

He was pissed off about Syria being bombed by Biden.

shooter may have been mentally ill.

Which game is this in, so I can look it up?

A metally ill Serian refugee (thank you Obama) on probation. 

Sounds like a perfect storm for violence.

Find out how he got the gun and correct that problem or arrest and charge whoever gave or sold him the gun.

Because when bad people get weapons they hurt people.

And when good people are deprived of weapons they get hurt.

If we impeach Trump again and make bb guns illegal, Amerika will be great again.

The shooter had mental health problems.

Not yet, apparently.