MIDDLETON, Mass. — Authorities think a suspect in a gruesome double homicide in Massachusetts is responsible for a knifepoint carjacking.Police say a man was carjacked outside a Middleton restaurant at about 7 p.m. Wednesday by a man they believe was Wes Doughty (DOW'-dee).Doughty is a suspect in the slayings last weekend of 37-year-old Mark Greenlaw and 39-year-old Jennifer O'Connor, whose bodies were found in a cluttered Peabody home.