In ruling that sufficient evidence exists to try Sweat, Okfuskee County Judge David Martin also ruled Sweat's 2011 videotaped statement to investigators may be used as evidence in the trial, the Tulsa World reported.
In the video, which was played during two days of hearings on whether Sweat should be bound over for trial, the defendant tells authorities he killed "two monsters."
"This is one of the saddest cases I've had in a long time," Martin said.
State investigator Brad Greene testified Whitaker, 11, and Paschal-Placker, 13, appeared to have been shot multiple times, probably with a larger-caliber pistol and a smaller-caliber gun. The girls were killed while out for a walk during a weekend sleepover.
Sweat is scheduled to be tried in June for the 2011 slaying of Ashley Taylor, a former girlfriend.
No date was set for trial in the deaths of Whitaker and Paschal-Packer. Prosecutors said they will seek the death penalty for Sweat.
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