Who were the killers of Imam Husayn(a.s)?

Source: Understanding Karbala, By: Allamah Sayyid Saeed Akhtar Rizvi
Time and again objection is issued by the ignorant that killers of Imam Husayn (a.s) were Shias. Though more than once those objections have been replied and refuted, yet once in a while the same voice is heard again. I would like to present a criterion by which truth and falsehood can be distinguished and any impartial, justice-minded person would have no difficulty in differentiating between truth and falsehood.
If we ponder upon the following three points there would be no problem in taking a decision:

(1) Which sect is in perfect agreement with the holy personalities and their deeds and which group is in opposition to them.
(2) Which sect considered Yazid to obligatorily deserve curse and in the view of which sect is he obligatorily qualified for obedience (or in whose view at least he should not be cursed)?
(3) Which sect observes aloofness and harbors hatred towards the military chiefs of Yazid and those who participated in the slaying of Imam Husayn (a.s) and which group considers them reliable in religious matters and takes narrational reports from them and praise and admire them?
After an inquiry into these three things a decision could easily be reached whether the killers of Husayn (a.s) are connected to the sect, which until today considers Yazid accursed and damned or to the sect with personages who shower praises on the military chiefs of Yazid and consider Yazid himself worthy of obedience.
The First Problem
Now we shall think upon the first problem: “Which sect is in perfect agreement with the holy personality of the martyr of Karbala’ and his deeds, and which group is in opposition to him.”
There is no need at all to say this regarding the Shias that they consider Imam Husayn (a.s) obligatorily worthy of obedience by the command of Allah, that he is appointed by Allah and was the true successor of the Prophet. They consider each saying and action of his as per the will of Allah. They consider his truce and battle the mirror of the best wisdoms and his rising and sitting a reflection of the Divine hidden wisdom. In view of Shias, Husayn (a.s) was a piece of Muhammadan effulgence. His flesh and blood were flesh and blood of the Messenger of Allah (s.a.w). Love towards him is obligatory on all. His obedience was a channel for perfection of faith. He was pure of every mistake and deviation. Loving him is recompense of prophethood:
Say: I do not ask of you any reward for it but love for my near relatives…1
His being is purified of every physical and spiritual filth and impurity:
Allah only desires to keep away the uncleanness from you, O people of the House! And to purify you a (thorough) purifying.2
He is the son of the Prophet.
Come let us call our sons and your sons and our women and your women and our near people and your near people, then let us be earnest in prayer, and pray for the curse of Allah on the liars.3
He is the flower of the Holy Prophet (s.a.w). He is from the Prophet and the Prophet is from him. His Imamate is neither based on an armed uprising nor allegiance of the people. He is the chief of the youths of Paradise. He was infallible since the beginning of his life until the last moments. The infallibility of the Holy Imam is the special belief of the Shias, which is not shared by any non-Shia sect. (Although many Ahl al-Sunnah researcher scholars consider them protected from sins).
As for the non-Shia sects, among them also all Hanafi, Shafei and most Hanbali consider Imam Husayn (a.s) on the right and Yazid on the wrong – quoting references here would unnecessarily prolong the discussion, hence I am just giving here a few names of scholars and the books in which they have mentioned those points:
(1) Allamah Qastalani (Shahabuddin Abul Abbas Ahmad bin Muhammad died 923 A.H..) – Irshad as-Saari Sharh Sahih Bukhari, Vol. 10, Pg. 139
(2) Ibn Jauzi (died 1200 A.D.), Ar Raddo A’laal Mutasibul Aneed al Maane min dhimme Yazeed
(3) Sibte Ibn Jauzi (died 1257 A.D.), Tadkeratul Khawaasul Ummah
(4) Allamah Ahmad bin Hajar al-Haithami (died 974 A.H.) Sawaiqul Mohreqa, Pg. 132-134
(5) Imam Jalaluddin Abdur Rahman bin Abi Bakr as-Suyuti (died 911 A.H.), Tarikhul Khulafa
(6) Allamah Taftazani (Saaduddin Masud bin Umar, died 1389 A.D.), Sharh Aqaid Nasafi
(7) Shaykh Muhammad Sabban (Muhammad bin ‘Ali, died 1792 A.D.), Isafur Raghibeen
(8) Shah Abdul Aziz Dehlavi (died 1824 A.D.), Madarijun Nubuwwah, Jazbal Quloob
(10) Maulana Abdul Hayy Farangi Mahli: Fatawi, Vol. 3, Pg. 7
(11) Nawab Siddiq Hasan Khan Bhopali (died 1889 A.D.), Baghiyatur Rayed Fee Sharhul Aqaid, Pg. 97
(12) Maulana Muhammad Mateen Farangi Mahli, Waseelatun Najaat, Pg. 290
(13) Mufti Muhammad Ikramuddin, Sadatil Kaunain fee Fazailil Hasnain
(14) Qadi Muhammad Sulaiman, Rahmatallil Aalameen, Pg. 233
This is a sample that includes names of Hanafi, Shafei and Hanbali scholars and who have clearly said that the steps of Imam Husayn (a.s) were on the right and that he was martyred in a state of oppression.
On the other hand there are those Hanbalis who consider Ibn Taiymiyah as their leader and they are Nasibis4 and Kharijis5 who in order to deceive the common people, call themselves Sunnis. Such people consider Yazid as a rightful caliph hence they think that Imam Husayn (a.s) was (God forbid) in the wrong and thus worthy of capital punishment, rather obligatorily deserving of being killed. In the present age, an example of such a person is Mahmud Ahmad Abbasi, who by writing, Caliphate of Muawiyah and Yazid has hurt the feelings of all the Muslims. In the past age even before Ibn Taiymiyah (died 728 A.H.), Abu Bakr Muhammad bin Abdullah Ibn Arabi (died 543 A.H.) had sung the same tune when he said:
“Husayn was not killed but by the sword of his grandfather (that is, as per the command of the Shariah) because the allegiance for Yazid had been paid before and Husayn had rebelled against it.”
This Ibn Arabi had lived before Muhiyyuddin Ibn Arabi (the writer of Futuhaat-e-Makkiyyah) and died in 638 A.H. The following statements of Tadkeratul Khawaas are about him:
Hafiz (One who has learnt the Qur’an by heart), Allamah (Most learned), Qadi (Judge), Faqih (Jurist) and on the position of Ijtihad, Abu Bakr Ibn Arabi was the student of Imam Ghazzali (died 505 A.H.). The same Imam Ghazzali who was famous by the title of Hujjatul Islam (Proof of Islam) and who is considered as one who strengthened the foundations of religion, and whose famous verdict (Fatwa) is that:
“It is unlawful to sermonize about Husayn and his companions because it leads to criticism of the companions.”