Flavius Josephus, The Wars of the Jews
William Whiston, A.M., Ed.

[254] When the country was purged of these, there sprang up another sort of robbers in Jerusalem, which were called Sicarii, who slew men in the day time, and in the midst of the city; this they did chiefly at the festivals, when they mingled themselves among the multitude, and concealed daggers under their garments, with which they stabbed those that were their enemies; and when any fell down dead, the murderers became a part of those that had indignation against them; by which means they appeared persons of such reputation, that they could by no means be discovered. The first man who was slain by them was Jonathan the high priest, after whose death many were slain every day, while the fear men were in of being so served was more afflicting than the calamity itself; and while every body expected death every hour, as men do in war, so men were obliged to look before them, and to take notice of their enemies at a great distance; nor, if their friends were coming to them, durst they trust them any longer; but, in the midst of their suspicions and guarding of themselves, they were slain. Such was the celerity of the plotters against them, and so cunning was their contrivance.