Adam Clarke on Genesis 34:25

On the third day, when they were sore - When the inflammation was at the height, and a fever ensued which rendered the person utterly helpless, and his state critical, Simeon and Levi, the half brothers of Dinah, took each man his sword, probably assisted by that portion of the servants which helped them to take care of the flock, came on the city boldly, בטח betach, securely - without being suspected, and being in no danger of meeting with resistance, and slew all the males. Great as the provocation was, and it certainly was very great, this was an act or unparalleled treachery and cruelty.