First let me tell here an Ayat from Quran: 

If any one slew a person - unless it be for murder or for spreading mischief in the land - it would be as if he slew the whole humanity: and if any one saved a life, it would be as if he saved the whole humanity.
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Today Death Toll In Karachi Bus Shooting Rises To 44 death and 13 injured

"At least 44 people have been killed and 13 others injured when some unknown gunmen attacked a passsenger bus near Safoora Chowrangi in Karachi, Dunya News reported.

 
Reportedly, sixteen women were among the dead.
 
"Six terrorists came on three motorcycles, they entered the bus and began firing indiscriminately. They used 9mm pistols and all those killed and injured were hit by the 9mm pistols,"

So who are they are these Muslim?