People who knew Devin Kelley, 26, the alleged Sutherland gunman, say he was judgmental and often posted rude or alarming comments on Facebook and other social media platforms.

Tyler Police Officer Don Martin told CBS19 if anyone notices any alarming behavior on social media, they should report it immediately to local police.

"It's best not to use social media and report it to us,” said Martin. “It's best to call us in person and give us some background that way we can ask several questions and dig a little deeper into what's going on."

Martin said staying vigilant and reporting disturbing behavior could help law enforcement stop a violent attack from happening.

“They've bought a bullet proof vest, they bought a high caliber weapon that they use to not have,” said Martin. “All those are red flags that law enforcement needs to know about."

Christi Lawson a licensed clinical social worker at ETMC told CBS19, behavior that can be considered alarming includes paranoia, agitation and isolation.

"It may be socially isolated,” said Lawson. “They may be in a crowd or large family but they may not have the ability or feel like they have the ability to talk to anyone."

Officer Martin said although the strange behavior isn't always against the law, police should still know about it.

“There's going to be times where they haven't really broken the law and there's nothing we can do, but that doesn't mean we don't put them on the radar screen," said Martin.

Martin said an investigation can include reaching out to the person and making a welfare check or offering psychological help.

"If there are so many red flags, then we will take it to another level," said Martin.

Officer Martin said if the person refuses help, but is believed to be a danger, officers may take that person into custody.