Before he killed 12 people at the Washington Navy Yard, Aaron Alexis carved odd messages onto the stock of his shotgun, officials say. One read “Better off this way,” while the other said “My ELF weapon,” according to officials involved in the investigation. It's not clear what was meant by the carvings, though ELF stands for extremely low frequency. Alexis told Rhode Island police in August that he was hearing voices and that three people were following him to keep him awake. He also said they were using “some sort of microwave machine” to send vibrations into his body.