This man is not a responsible gun owner or man who was defending his life (except at the very start). He acted out cold-blooded murder when the threat was already neutralized.
It is in the interest of gun rights and of basic human morality to condemn what he did. If what we know so far is true, he should never leave a cell again.
That said, innocent until proven guilty.
Beretta PX4; 92FS; 92S; 8040G | Sig Sauer SP2022; P6 | Glock G19 Gen4; G23 Gen3| Colt Python 4"; 1968 Detective Special 2"| Smith & Wesson M642-1 | Ruger LCP; 10/22 | Daniel Defense M4V1 | Remington 870 | Alpine M1 Carbine | Steyr M1895 |1943 Izhevsk Mosin M91/30 | Walther PPS