Circumstances surrounding the death of a 47-year-old Stow man whose body was found in Lake Boon on Saturday do not appear to be suspicious, according to the Middlesex district attorney’s office. Authorities are not releasing the man’s name and the investigation is ongoing, according to Stephanie Guyotte, a spokeswoman for the district attorney. The man went missing around 11 p.m. Friday and was believed to be in the lake, State Police said in a previous statement. The State Police dive team located his body around 5 p.m. Saturday, shortly after they began a search of Lake Boon, which lies partly in Stow and partly in Hudson. The man’s body was transported to the office of the chief medical examiner in Boston.