ויעקב שמע כי טמא, Shechem, who had already been mentioned (hence his name does not need to be repeated here and a pronoun will do) and that as a result of what he did, Dinah had been defiled by an uncircumcised person who had been intimate with her.
Radak on Genesis 34:5
Radak, in his commentary on Genesis 34:5 makes a point to draw out how terrible Shechem was.
"AND HE WASN'T EVEN CIRCUMCISED!!"