Terry Allen Miles was convicted Tuesday. Investigators say the 45-year-old was living with the woman in Round Rock to help look after her two daughters when they disappeared in December 2017.
An officer later found their mother dead from blunt-force injuries. Miles and the girls were found days later in a remote area of Colorado. The girls were 7 and 14 at the time.
Investigators allege Miles repeatedly struck the woman with a flashlight, though he hasn't been charged in the death. Defense attorneys say Miles was protecting the girls from their mother's chaotic and illicit lifestyle, and had no part in her death.
Miles faces up to life in prison when sentenced in April.