If there is any member of any religion doing such bad things in the world, such as Murder, in the Name of that Religion, then the religion must be suspect. Yes. The person need not be suspect, he is the criminal.
People get confused and go around the mulberry bush many times with this logic. Allow me to take it apart so we all could see. There are three possibilities here, both leading to the very same crime.
Case A ) Murder, not religiously motivated .
If a Muslim kills an American because he hates USA, he hates the arrogance and the show-off of Americans, then that's personal. He just happens to be a Muslim. It ain't nothing to do with religion.
A biased person will insist it is due to religion, and would still insist, despite clear evidence, that it has something to do with Islam. That is why I say those not trained in science and those not equipped with professional analytical tools will find it difficult to analyse Islam correctly and usually conclude wrongly. Best of all, usually these people insist they are right.
Case B ) Murder, not religiously motivated, but using religion as an excuse, a tool.
If he kills because he says Allah asks of him to kill all infidels, and it is required of him in his Religion, and that he will be rewarded with heaven and virgins and what not, then, that's religion !
But then, again, is he telling the truth ? What he is saying about the religion is true, but why does he want that particular person dead ? It could very well be personal vendetta.
Again, this is hatred, using Islam as a convenient tool. Islam is hijacked.
Case C ) Murder, religiously motivated, using religion and al the tools of the religion.
There are people who kill because he says Allah asks of him to kill. Typically, they see it as a ritual, or religious duty and scream " Allahu Akbar" upon completion.
When Muslims go to war with Muslims they both shout "Allahu Akbar", which is the Muslim war cry. This is purely religion. It may be political, but the dispute is usually religion or turn religious. Shias and Sunnis cannot reconcile, and as at this writing is engaged in a proxy war in Yemen. It's Saudi versus Iran, It's Sunni verses Shia. Muslims killing each other.
In short Islam is a very effective tool to engage in War, the very Doctrine and everything about Islam prepares one to die for Allah, in the hope of heavenly rewards, This is the very core engine of Islam, and is what the Terrorists use.