Islam is a message to all the mankind and for all the time. Islam is based on Qur'an and the tradition of the Messenger and slave of Allah, Muhammad ibn Abdullah (Peace and blessing upon him) to whom Qur'an was revealed. The revelation is complete and the religion of Islam is complete with the death of the Messenger. Islam is free from imperfections and it was revealed to the humanity to follow. However, human beings are not perfect. They make mistakes. All the muslims strive to follow the perfect teachings of Islam.
So what does the perfect teachings of Islam say? The muslims follow the Qur'an and the Qur'an says (emphasis mine):
... whoever kills a soul unless for a soul or for corruption [done] in the
land - it is as if he had slain mankind entirely. And whoever saves
one - it is as if he had saved mankind entirely. And our messengers
had certainly come to them with clear proofs. Then indeed many of
them, [even] after that, throughout the land, were transgressors.
From the traditions of the Prophet of Islam i.e. hadeeth (which is another source of Islam), it is said:
Ibn 'Umar (May Allah be pleased with them) reported: Messenger of
Allah (sallallahu 'alaihi wa sallam) said, "A believer continues to
guard his Faith (and thus hopes for Allah's Mercy) so long as he does
not shed blood unjustly". [Al-Bukhari]
Islam is a forgiving religion and asks the muslims to establish justice between themselves and with others. It prohibits oppression. There are several hadiths of the Prophet (peace be upon him) where he advices muslims that oppression is prohibited, so do not oppress anyone and the one who does so is a transgressor against Allah. Islam also places a great emphasis on kindness and virtues. Islam asks us to show forgiveness, enjoin people in good and forbid what is wrong. It says that God loves those who pardon and do good and warns people against extremism. There are several verses in Qur'an which warns muslims of extremism:
...do not commit excess in your religion or say about Allah except the
truth. [Surah An-Nisa:17]
And in another verse asks us to not follow those who call to their desires.
Unfortunately, terrorism happens. It happens in all societies because sometimes muslims are ignorant about what their religion tells them. This world has various elements of ignorance, injustice and oppression. Terrorism takes the form of individuals, groups and even sometimes, states. Terrorists do not take their motivations or inspirations from Islam but from elsewhere. They call towards their desires. Islam is not at fault. The terrorists usually have a political motivation and they misquote Qur'an to gather fame and crowd. Suicide bombings, hijackings or kidnappings are not a part of Islam. Islamic scholars have given verdicts against such acts of terrorism and they have voiced their opinion against the perpetrators of this crime. These are acts of corruption and Allah says in Qur'an that he does not like those who spread corruption in land:
And when he goes away, he strives throughout the land to cause
corruption therein and destroy crops and animals. And Allah does not
like corruption. [Surah Al-Baqarah:205]
One thing we should remember is that among those killed in the 9/11 incident were also innocent muslims. How can the terrorists justify their killing when murder is a major sin? This verse in Qur'an asks muslims not to kill one another or themselves. Then how is suicide bombing or any kind of bombing justified? Indeed they are lying against Allah and the messenger and Qur'an says those who invent lie against Allah are sinners.
Like you, there were many people who got interested in Qur'an after incidents like these and they sincerely read Qur'an and found the reality of Islam and became muslims. They found that the Qur'an is completely against what the terrorists claim. The Prophet said "The Qur'an will either be a proof for you or against you". The Qur'an is a proof against the terrorists. We hope, you also, sincerely read Qur'an and discover the truth about Islam.