US police hunting the killer of four Muslim men in a New Mexico city said on Tuesday they have arrested their “primary suspect” in the case. Detectives in Albuquerque had appealed for public help in cracking the mystery behind the violent deaths of the men, all of whom were from South Asia. The appeal came after the discovery on August 5 of a body near an office providing services to refugees. A 27-year-old man was found on August 1, less than a week after the police began investigating the murder of a 41-year-old. The November killing of an Afghan man in the city was also being probed for a l…