Someone, who commits acts of terrorism, even if committed in the name of Islam, does not deserve to be called Muslims.
Indeed, the true Islam is that which contained in the Qur'an (Holy book of Islam) and in the Sunnah (The sayings of the prophet Muhammad SAW). And not everything that is said to be Islam is in considered part of the religion of Islam. It needs to be returned to the Qur'an and to the Sunnah.
Allah, the Most Merciful, said:
"And do not kill those souls whom Allah has prohibited unless justified by a due legal right" (Surah Al-An'am 6:151)
The Prophet of Muhammad (SAW) said, in an authentic hadeeth by Imam al-Bukhari,
"Whoever kills a non-Muslim who has an agreement with the Muslims then he will not smell the fragrance of Paradise"
In the other authentic hadeets by al-Bukhari, The Prophet of Muhammad (SAW) also said,