Dallas County District Attorney Craig Watkins says he'll seek the death penalty in the capital murder case of a 30-year-old man charged with last month's rape-slaying of a 16-year-old suburban Dallas girl.
Authorities say Franklin Davis already was charged with four counts of sexual assault when he took Carrollton high school sophomore Shania Gray from her school.
She had been expected to testify against him at his trial on those charges and police believe she was killed in order to silence her testimony.
According to Davis' confession in the affidavit, he picked up Gray on the afternoon of Sept. 6 and drove her to the trail head at Champion Trail near Valley View Lane and Interstate 635.
Davis told police Gray spotted a .380 pistol in his possession along the way and asked if he was going to hurt her. He said he told the girl he only wanted to talk about the case. Once at the trail head, Davis led Gray down the trail to the Trinity River, where he shot her twice with the pistol, he told police. Davis told police that the teenager asked him, 'Why?' as she partially fell into the Trinity River, clinging to life, before he strangled her with his foot.
In the affidavit, Davis said he won Gray's trust with a fake social media profile and a prepaid phone. Posing as someone else, he convinced Gray to meet him at the school, he said. Davis told police that when he arrived at the school, Gray was surprised to see him.
Davis was indicted on the murder charge Wednesday. Gray's body was found along a fork of the Trinity River on Sept. 8.
NBC 5's Frank Heinz contributed to this report.