A 17-year-old arrested for allegedly murdering his mother in Polk County has been charged as an adult with first-degree murder and kidnapping.The Polk County Sheriff's Office said the teenager allegedly murdered his mother, Catherine Griffith, 39, of Port Charlotte, on September 8.In a press conference shortly after the killing, Polk County Sheriff Grady Judd said nearby witnesses saw the teen and his mother fighting outside his grandmother's house in Auburndale, followed by the teen dragging his mother into the home by her hair around 4:30 p.m.The witnesses said they heard the mother repeatedly say, "Let me go." The teen's grandmother was not home when the incident took place.Around two hours later, PCSO received a 911 call from the teen who said that he and his mother had a long fight and she fell on a knife and was bleeding from the neck, Sheriff Judd said. The teen was given instructions on how to do life-saving techniques. When detectives asked the teen what happened, he allegedly became uncooperative and asked to talk with a lawyer. Detectives also noticed inconsistencies in the teen's story during the 911 call and what was discovered at the scene.According to the indictment, Catherine Griffith was stabbed to death with a knife.Judd said that just over a year and a half ago, the teen allegedly killed his father, Charles Griffith, in Oklahoma. The teen claimed self-defense and said that his father pulled a knife on him first. The teen was initially charged with first-degree murder, but the charges were dropped after prosecutors said they could not disprove the teen's claim of self-defense.The teen had allegedly threatened to kill his mother on multiple occasions, Sheriff Judd said. In November of 2023, the teen was charged with domestic violence battery against his mother by the Charlotte County Sheriff's Office.The teen's grandmother told the Polk County Sheriff's Office about several occasions in which the teen was verbally or physically aggressive with his mother in the past.