Sort of an odd way to pose the question--the means of a murder happen generally according to what's convenient, unless the murderer has some sort of particular MO. Masters were sometimes murdered at the hands of their slaves, although it was rare--more common were slave revolts like the three Servile Wars, although slave revolts rapidly died down, more or less disappearing in the Principate. We know of several cases of slaves murdering their masters outside of servile revolts--most famous is probably the murder of the city prefect Pedanius Secundus by his slaves in 61. Secundus' murder illustrates quite plainly what must have been one of the major reasons that we hear much more often about runaway slaves than slaves who did harm to their masters. By Roman law a slave who failed to come to the aid of his master if his master's life was in danger was a criminal, and the guilt for the murder of a slave's master was shared equally among the entire household. As a result--and despite the protests of the people--the entire household, all 400 slaves, were put to death at once.