premise: Achillas (Greek: Ἀχιλλᾶς ) was one of the guardians of the Egyptian king Ptolemy XIII Theos Philopator, and commander of the king's troops, when Pompey fled to Egypt in 48 BC. He was called by Julius Caesar a man of extraordinary daring, and it was he and Lucius Septimius who killed Pompey at the suggestion of the eunuch Pothinus and Theodotus of Chios.
hypothesis: Achillas only killed one person.
reason: It doesn't say how many people he killed in his life. It may have been many. Or it could have been one... no way to know.