Parliament can prescribe different elements to the offence, including different mens rea for different modes of commission of the offence, one of which is wilfully, one of which is by negligence. In prescribing what would constitute negligence, one would rely on judicial interpretation. In this case, contrary to what was suggested earlier, it would be a marked departure from the norm.
In any event, one doesn't convict or sustain a conviction of anyone of a criminal offence, including offences for the service offences, without all the essential elements being made out beyond a reasonable doubt.