Former Sangamon County Deputy Sean Grayson shot and killed Massey inside her Springfield home earlier this month after Massey called 911 to report a possible intruder.
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Sangamon County Sheriff Jack Campbell spoke on Monday during a listening session held by the U.S. Department of Justice.
"I can't imagine the pain that her family and friends feel right now, I'm sorry, she called for help and we failed her. That's all she did, that's all she did was call for help. I'm going to say something right now that I've never said in my career before, that we failed, we did not do our jobs," Campbell said.
Grayson, who was fired from the department, has been charged with Massey's murder.