(Please cite your source, if any.)
Interestingly, Daas Zekeinim and Kli Yakar (to Gen. 32:8) say that when Yaakov heard that Eisav was planning to attack, he was distressed thinking that this must mean that indeed Yitzchak was already dead and that Eisav therefore feels free to kill him.
Rashbam (to 32:7) suggests that indeed Eisav meant well in coming out towards Yaakov with his 400 men - he meant them as an honor guard for him - but that Yaakov suspected that his intentions were in fact evil.
Ramban (to 32:8) writes that Eisav didn't specifically say that he intended to harm Yaakov, but that Yaakov's messengers figured this out by talking to his men. According to this latter approach, it could be that Eisav in fact wasn't planning to kill Yaakov outright, just to scare him (maybe enough so that he'd die of a heart attack or something, without having to actually lay hands on him? After all, Eisav did always try to hide his evil deeds with a veneer of innocence - see Rashi to Gen. 26:34).
Lavan sent his son Beor (the father of Bilam) who was 17 years old - with 10 men to let Eisav know that Yaakov was on his way back. Beor also told Eisav how Yaakov fooled his father Lavan just like he fooled Eisav. That got Eisav riled up and he went to greet Yaakov with 400 men. (Sefer HaYoshor - end of Parshat Vayeitzei)