A nationwide manhunt is under way for the gunman believed to have killed a Cotten Apartment resident in his home Friday night.The suspected murderer, Gregorio Arenas, is considered armed and dangerous and is wanted on criminal homicide charges.He was added to the TBI’s Top 10 Most Wanted list Tuesday afternoon with a $1,000 reward for information leading to his arrest.Arenas is described as 5-foot-3 and approximately 125 pounds. He was last seen driving a red Pontiac with Tennessee tag 555-JPH. His last known address is 1350 Viola Road, McMinnville.The victim, Albertano Guerro Trejo, 29, was shot dead in his Cotten Apartment residence off Cascade Avenue around 9:30 p.m. Friday. He was killed by a single shot to the chest from a 9mm handgun allegedly wielded by Arenas.