Stop right there. Soldiers can be murderers.
GIYF: William Laws Calley Jr.
FTFY
Soldiers can be murderers, but I would argue that not when filling commands in a
just war.
I suggest you read further down through Maimonides, where you will see that there are specific ways of how war is to be waged and conducted.
I will also point out, that despite several opportunities, it was only once (IINM) that a Jewish king waged a war on Amalek, for the purpose of total annihilation, and at that time was commanded by a prophet to do so (Maimonides also discusses at length the qualifications of a true prophet).