ONAWA, Iowa (AP) – Authorities say a Monona County woman held her infant son under a bathtub faucet to drown him.  Twenty-four-old Ashley Cameron, of Onawa, has been charged with first-degree murder in the death of her 15-month-old son, Markis Dahms.  Assistant Onawa Police Chief Jim Fouts said Thursday that investigators believe Cameron acted alone. Fouts says Cameron “was with Markis during the time of his death, and she was the sole caregiver for Markis.”  Officers were sent to the Onawa home on Feb. 11th because of a report that a toddler wasn’t breathing. Fouts says Cameron wasn’t arrested until all the autopsy results had been obtained.  She remains jailed pending $1 million bail.  Cameron’s 2-year-old daughter is being cared for by relatives.