Rashi on Genesis 34:13/רש"י על בראשית ל״ד:י״ג

1במרמה WITH GUILE — cleverly

2אשר טמא BECAUSE HE HAD DEFILED — Scripture (the Sacred Historian) says that there was no deception (מרמה) in this because he had defiled Dinah their sister (Genesis Rabbah 80:8).