Shias in the world, and unfortunately some small amount of sunnis are confident that Yazid was the only one person who was responsible for murdering of Husayn (r.a).
But this is not true.
Let us see who was accused by Husayn (r.a) himself in regards to this crime.
In “Muntahal Amal” by sheikh of shias Abbas Qummi (1/535), we can see Husayn saying to people who inviting him to Kufa:
اللهم أحكم بيننا وبين قوم دعونا لينصرونا فقتلونا
Translation: O Allah! Judge between us and people, that called us (here) to help us and then killed (fought) us.
Check any known historic shia or sunni books. That was shias of Kufa that called Husayn (r.a) to their city, and then due to fear, hypocrisy, money they betrayed him and killed him.