Accused Oxford High School shooter Ethan Crumbley plans to plead insanity in the criminal case accusing him of killing four students and wounding six others and a teacher during a Nov. 30 attack, according to a court filing Thursday. Crumbley, 15, a sophomore at the high school, has pleaded not guilty to accusations he committed the nation’s deadliest school shooting since 2018. A one-sentence notice of insanity defense was filed early Thursday in Oakland Circuit Court, signed by defense attorneys Paulette Michel Loftin and Amy Hopp. Neither have returned telephone calls. “Please take notice t…