The man whoin a Florida supermarket on Thursday had made repeated threats online, according to the sheriff.
"There was a chance this could be stopped," Palm Beach County sheriff Ric Bradshaw said Friday. "You know why? The reason is, he is on Facebook. He has said, I want to kill people and children. You think a damn soul told us about that? No."
Surveillance cameras captured the entire incident, which lasted less than four minutes, according to police.
Just before noon on Thursday, the grandmother parked the shopping cart holding her young grandson as she was looking at items when the 55-year-old gunman, Timothy Wall, walked up.
"He pulls out his gun and walks over from one aisle to the next, where the child was parked in his shopping cart," Palm Beach County Sheriff's Office major Talal Masri said.
He shot the child and then turned toward the grandmother.
"The grandma instinctively jumps in and tries to stop him. She struggles with him, his gun jams, he was able to overpower her and push her down to the ground. He shoots her down while she's on the ground," Masri said.
Wall then shot himself. He did not know the victims. Police said that he had declared bankruptcy earlier this year and his ex-wife told them he recently started acting strangely.