Last Updated Feb 16, 2018 9:22 AM EST
New questions are emerging as to whether officials and friends missed warning signs about suspected Florida gunman Nikolas Cruz. His Instagram page featured several photos of weapons, including one with a gun and knives. A law enforcement source tells CBS News the Broward Country sheriff's office was told in February 2016 that a post on Instagram under Cruz's name said he was going to shoot his school, but the sheriff told our Miami station WFOR he was unaware of such notification.
Cruz moved into a home with a friend in November after his mother died. He had lived in another home nearby. Police were reportedly called there 39 times, beginning in 2010, for calls ranging from domestic disturbance to abuse. Those signs of troubling behavior weren't unnoticed, reports CBS News correspondent Jericka Duncan.
"My sister had texted me and said it was Nikolas Cruz. And I said, 'Oh my god, I know him!'" said Sarah Lowy, who says she knew Nikolas Cruz from his job at the Dollar Tree store.
"He had this weird disposition about himself," Lowy said. "He followed me on Instagram. … And I saw all of the pictures of his guns, he had a picture of his gun up to his face."
Lowy said she regrets not doing more.
"As soon as I heard what happened, immediately in my mind was I should have done something. I could have prevented this," Lowy said.
Seventeen people were killed at Marjory Stoneman Douglas High School in Parkland, Florida, when the gunman opened fire. More than two dozen others were wounded.
People who knew Cruz said he spoke about his guns and hurting animals. Shelby Speno lived next door to Cruz.
"I saw him with the gun aiming at their chickens," Speno said.
President Trump tweeted on Thursday: "Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!"
Ben Bennight, a Mississippi bail bondsman, saidwhen he noticed a comment on one of his YouTube videos that troubled him. "I'm going to be a professional school shooter," it said, posted under the username "nikolas cruz." The FBI visited Bennight the next day.
"Anybody that makes a public statement like that definitely needs to be investigated," Bennight said.
But on Thursday, the FBI said the post was a dead end because it lacked specific information about the time, location and identity of the person who posted it.
"No additional information was found to positively identify the person who posted this comment," said Robert Lasky, Miami FBI special agent.
After the Columbine High School shooting in 1999, the U.S. Secret Service published a handbook for law enforcement detailing how to prevent school attacks. The study finds there isn't a specific trait or behavior that can help determine if a student is planning a school shooting.