the Smith and Jones episode of Doctor Who (which
kicked off Series 3), the Judoon won't take action against
Florence for having apparently killed the Doctor, because
they think she is a human and they have no jurisdiction over
humans. Why, then, did they earlier disintegrate a human being
for allegedly assaulting one of their officers?
most likely explanation is that the Judoon are permitted to
pass judgement on any creature that commits an offence against
them, the Judoon. Therefore they are able to carry out that
summary execution for the alleged assault. The apparent murder
of a member of another species (the Doctor) by an apparent
human being (Florence) is another matter entirely and no concern
Alternatively, the Doctor does state that the Judoon are stupid,
so maybe they just forgot their own rules for a moment there!