"The senseless deaths of these two little girls broke our hearts yet hardened our determination to hold responsible the people whose recklessness killed them," District Attorney Jeff Rosen said.
The 28-year-old banker whose death led to "vitriolic online attacks" on Jefferies died from the "toxic effects" of fentanyl and cocaine, the Dallas medical examiner said.
"Both medetomidine and xylazine are earmarked for veterinary use and therefore face less rigorous regulation processes than substances made for humans, which could explain why they're becoming more common in the recreational drug supply."