1. Some translations of the Bible used the word “kill” instead of the word “murder”
Unfortunately, this is not a good translation – why?
The original Hebrew scripture used the word most closely associated with the English word “murder” - the intentional, premeditated killing of another person with malice.
Virtually all biblical scholars agree that this was the intended meaning of this commandment

2. Most Jewish commentators believe that Mattathias should not be considered guilty of murder – he killed the representative of the king who was about to kill his people
It doesn’t mean that what he did wasn’t sin, however.
Perhaps it’s best summed up by one rabbi as “…a necessary evil”.