Eight months after the death of Gibbs's husband, she poisoned her youngest son, also named Marvin. He was assumed to have inherited a liver disease from his father although his death certificate listed hepatitis. Gibbs was not suspected of any wrongdoing and she again donated a large portion of her life insurance payout to the local church. In January 1967, another one of Gibbs's sons, 16 year old Lester, died suddenly. Doctors listed his cause of death as a rare muscular disorder and for a third time, Gibbs donated life insurance money to the church.