US police hunting the killer of four Muslim men in a New Mexico city said on Tuesday they have arrested their “primary suspect” and charged him with two of the murders. The killings, three of which came in the last couple of weeks, had sent shock waves through the Muslim population in Albuquerque, with community leaders talking of a growing sense of panic. But on Tuesday, investigators said a public tip had led them to 51-year-old Afghan immigrant Muhammad Syed. The breakthrough came after detectives had appealed for public help cracking the case, issuing a photograph of a car they believed wa…