James Elmore Jr. was found guilty of manslaughter connected to the deaths of Laura Miller and Audrey Cook.
A jury in Galveston reached the verdict more than four decades after 16-year-old Laura Miller disappeared.
Elmore was accused of providing a fatal dose of cocaine to his alleged accomplice, Clyde Hedrick. Hedrick is believed to have killed Miller back in 1984.
As reported by our tv partner, KPRC channel 2, Texas EquuSearch founder Tim Miller delivered emotional testimony to the jury. Laura Miller was his daughter.
"Knowing that your client mixed up the dope and handed that damn deal to Clyde Hedrick to go ahead and shoot up my daughter and take her life," Miller testified. "Yeah, your client deserves to be held responsible for that."
The sentencing phase begins on Thursday. Elmore faces up to 20 years in prison.