Why would Yusuf Ibrahim cut off two Coptic Christians' heads and hands -- and knock out their teeth?

I read an interesting article by Daniel Pipes in which he pointed out that in the United States we have had many

potential instances of jihadi violence in which the Establishment has colluded to sweep the Islamic dimension under the rug, treating the perpetrators as common criminals whose biographies, motives, and connections are of no interest and therefore remain unknown.

Pipes mentioned the pending criminal case of a Jersey City Muslim named Yusuf Ibrahim. Pipes noted that Ibrahim had allegedly shot and killed two Coptic Christians, cut off their heads and hands, knocked out their teeth, and then buried them in Buena Vista Township, New Jersey.

Yusuf Ibrahim is a Muslim, but can Islamic Doctrine actually support such actions? Islamic Doctrine is based on the commands of Allah found in the Koran and the teachings and example of Muhammad. So let’s see what Islamic Doctrine has to say about this.

In terms of killing the Christians, we have 9:5, the Verse of the Sword, which commands Muslims to kill non-Muslims. Simple enough. And, as we know, Islamic Doctrine supports beheading people: we have two verses in the Koran commanding it (8:12 and 47:4), and the example of Muhammad, who supervised the beheading of 600-900 captured Jewish males and also ordered, and approved of, the beheading of numerous individuals. In terms of cutting off hands, we again have the example of Muhammad, who on one occasion ordered the hands and feet of particular individuals to be cut off (Sahih Al-Bukhari, No. 233), and who for years had a standing order for his Muslim warriors to cut off the hands and legs of an individual named Habbar bin al-Aswad (The Life of Muhammad: Al-Waqidi’s Kitab al-Maghazi, p. 422). But what about knocking out teeth?

Here we can look to Abu Bakr, Muhammad’s close companion and father-in-law. After Muhammad died, Abu Bakr became the first of the four “Rightly Guided” Caliphs; these first four caliphs were so named because they are believed to have held the most firmly to the teachings of Muhammad. Abu Bakr started holding fast to some of those teachings soon after Muhammad died:

It is reported that certain women at an-Nujair having rejoiced at the death of the Prophet, abu-Bakr wrote ordering that their hands and feet be cut off. Among these women were ath-Thabja’ al-Hadramiyah, and Hind, daughter of Yamin, the Jewess.

The Origins of the Islamic State, Being a Translation from the Arabic, Accompanied with Annotations, Geographic and Historic Notes of the Kitab Fituh Al-Buldan of Al-Imam Abu-L Abbas Ahmad Ibn-Jabir Al-Baladhuri, p. 155

And also soon after Muhammad’s death, two singing women appeared before Al-Muhajir, the Muslim governor of the Yemen. One of them sang a song reviling Muhammad, and Al-Muhajir had her hand cut off and a front tooth pulled out. Abu Bakr wrote to Al-Muhajir:

I have learned what you did regarding the woman who sang and piped with abuse of the Apostle of God. If you had not beaten me to (punishing her), I would have ordered you to kill her, for the punishment (for abuse) of prophets is not like (other) punishments. So whoever does (something like) that among those claiming to be Muslims is (actually) an apostate; or among those claiming to be at peace with the Muslims is (actually) at war (with them) and a traitor…Now then: I have learned that you cut off the hand of a woman because she sang satirizing the Muslims, and that you pulled her front tooth. If she was among those who claim (to have embraced) Islam, then (it is) good discipline and a reprimand, and not mutilation.

The History of al-Tabari: The Conquest of Arabia, pp. 191-192

So even though the “Establishment” might be puzzled about the motives of Yusuf Ibrahim, we can see that Islamic Doctrine is fully supportive of killing Christians, cutting off their heads and hands, and even knocking out their teeth.