A Texas teen allegedly planned to shoot his 15-year-old ex-girlfriend outside of school "but changed his mind" and went to her house instead to kill her mom, 9-year-old brother and 13-year-old sister, according to cops.

"It was such a tragic and cowardly act of violence," Odessa Police Chief Mike Gerke said during a Wednesday media briefing on the triple slaying, according to local NBC affiliate KWES . "It's the kind of thing that really marks a community," the top cop said. "Particularly in this holiday season, it's a hurtful, horrible thing."

Police say the 15-year-old, whose name is being withheld by authorities due to his age, went to his ex-girlfriend's home at 8740 Hunter Miller Way in Odessa on Tuesday and barged in with a handgun. He allegedly shot his ex's mother, Jessica Rodrig

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