A 16-year-old boy is being charged in the death of his 10-year-old sister, Isabella Heffernan.The investigation took place in Fountain, Florida, roughly 30 miles north of Panama City. Isabella was last seen around 10 p.m. Saturday, and her family reported her missing around 11:30 a.m. the next day. The Bay County Sheriff’s Office found Isabella’s body in an open field behind her house around 4:20 p.m. Sunday. Authorities didn’t say what led them to arrest Isabella’s brother, 16-year-old Fredrick Matthew Lochridge. He’s been charged with an open count of murder.