Other source:
Goku, Gohan, Vegeta, and Shin are left wondering why Dabura suddenly stopped the fight. Suddenly, Babidi tries to take over Vegeta's mind. Although he is urged to fight it, Babidi's magic is too strong, and Vegeta's impure heart gives in. Now with Babidi's "M" on his forehead, he has turned evil. Babidi transports them all back to the World Martial Arts stadium where he instructs Vegeta to kill his friends. Vegeta refuses, as he apparently has not lost complete control of his mind. He says that his only goal is to fight Goku. To bait Goku into fighting him, Vegeta destroys part of the stadium, killing many fans.
