Here are some points why Kattappa Killed Baahubali.
Prabhas (Baahubali) loves Anushka (Deva Sena) who is from thieves country. Ramya Krishna (Sivagami) doesn’t like that and ask Baahubali to choose the Kingdom or Anushka and Prabhas leaves the kingdom for Anushka. Meanwhile, Kalakeya brother attacks on Mahishmathi kingdom and Prabhas saves the kingdom from Kalakeya brother. Prabhas and Anushka return to the Kingdom after the war with Kalakeya brother. Ramya Krishna doesn’t want Anushka to see as Queen and ask Katappa to kill Baahubali. Story writer Vijayendra Prasad recently said in an interview, ‘why everyone thinks that Kattappa killed Baahubali, he just stabbed him’, which is a new twist for the Baahubali 2.
So, we have to wait for the Part 2 to get to know what happened exactly and who killed Baahubali!!