Most assume that the killer of al-Ḥusayn was Shimr bin Ḏī al-Jawshan, while the authentic Sunni report, in Muʿjam al-Ṭabarānī 3/709, identifies the killer as Sinān bin Anas al-Nakhaʿī. The most authentic Shia report, via Abū Mikhnaf p. 146, identifies him as Sinān too.

@Farid_0v Who instigated the killing is more important than who dealt the final blow. ‘I shall remain covered in blood until I meet the Prophet (P) and I will say to him: Abu Bakr & Omar killed me’