Peter Placker testified in Okfuskee County District Court he and his wife were searching along a road after their granddaughter, Taylor Paschal-Placker, 13, of Weleetka and her friend, Skyla Whitaker, 11, also of Weleetka, when he spotted their bodies, checked them for a pulse and walked to the middle of the road, "screaming [my] head off."
"They killed our babies," he said he yelled.
Placker said one of the paramedics who arrived noticed shell casings on the road, the Tulsa World reported.
Kevin Joe Sweat is charged with first-degree murder in the shooting deaths of the two girls, who were killed while out for a walk during a weekend sleepover.
State investigator Brad Greene testified each girl appeared to have been shot multiple times, probably with a larger-caliber pistol and a smaller-caliber gun.
Sweat occasionally took notes and asked his attorneys questions during the hearing.
Sweat also is to be tried in June in Okfuskee County for the July 2011 slaying of a former girlfriend, Ashley Taylor, who disappeared that summer after they left Henryetta to get married.
Sweat, who has pleaded not guilty in both cases, could be sentenced to death if convicted.
The judge handling the pretrial hearing had not ruled on a defense motion to suppress incriminating statements Sweat made to investigators in September 2011.