The FBI receives countless tips and doesn't have the resources it would need to follow every lead, but the bureau appears to have "dropped the ball" after it was alerted that someone with the user name Nikolas Cruz posted on social media that he aspired to be "a professional school shooter," according to a former member of the FBI's Joint Terrorism Task Forces.

Steve Rogers, who said he supervised many investigations, believes the FBI could have tracked down Cruz last fall when 36-year-old Ben Bennight of Mississippi emailed the FBI a screenshot of the comment on a YouTube video and called the bureau's Mississippi field office. Agents interviewed Bennight the next day, asking if he knew anything about the person who made the comment, and that was the last he heard of them until they contacted him Wednesday, after Cruz, 19, allegedly opened fire at Marjory Stoneman Douglas High School in South Florida, killing at least 17 people.

Rogers said in an interview Thursday with Fox News that if he had come across a declaration on the Internet "that profound," he "would have sent officers to the house and at least begun an inquiry."

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He said he believes the FBI "dropped the ball" in this case, but he quickly added that the FBI receives "millions" of such tips from the Internet.

Nevertheless, Rogers said he would have made it a priority, tracked down Cruz, sent officers to his house and asked to be invited in for a chat. If invited in, he said, officers might observe evidence that could form the basis for a warrant to search computers and other digital devices.

Special Agent Rob Lasky, in charge of the FBI's Miami division, told reporters Thursday that after conducting database reviews of the "professional school shooter" comment, the bureau could not identify the user.

"No other information was included in the comment which would indicate a particular time, location or the true identity of the person who posted the comment," the FBI said in a subsequent statement.

'Just too often the case'

Attorney General Jeff Sessions, speaking to the Major County Sheriffs' Association Thursday, said it is "just too often the case that the perpetrators have given signals in advance."

"I suspect it appears that we have seen that again in this case," he said, referring to Cruz.

Sessions acknowledged that officers can't arrest somebody "that somebody thinks is dangerous." But he said the law enforcement community still needs to "do better."

The FBI said it is reviewing its handling of the case.

Meanwhile, Broward County Sheriff Scott Israel said Thursday he wants law enforcement to have the power to detain people over their social media postings.

Rogers told Fox News "the one common thread in all these shootings is social media."

"Somebody either heard something, saw something, chatted with someone in a chat room with regard to crimes like this," he said.

Asked to specify would kinds of actions or comments would warrant a law-enforcement response, Rogers turned attention to President Trump's remarks from the White House Thursday morning regarding the shooting in which the president mentioned the importance of God, family and faith.

"We need to get our families back together," Rogers said. "We need parents to understand that they've really go to get engaged with their children and keep an eye on them."

One day before the massacre in South Florida, a woman in Everett, Washington, called police after reading in her grandson's journal that he intended to commit mass murder at a local high school, the Seattle Times reported.

The 18-year-old student, who was arrested at his school, said he had learned from other mass school shootings, wanted to make the body count as high as possible and wrote he couldn’t "wait to walk into that class and blow all those (expletives) away."

"We are really grateful to the grandmother. It couldn't have been easy for her to do," said Andy Muntz, a spokesman for the Mukilteo School District. "It speaks to the importance of the saying, 'if you hear something or see something, call authorities,' and that's what she did. It’s quite possible she saved many lives including her grandson's."

Nikolas Cruz's adoptive mother died of pneumonia in November at the age of 68, and he had lived with two different families since then, the South Florida Sun-Sentinel reported. He was expelled from school last year for disciplinary reasons and was said to have had a "very disturbing" social media presence.

Public defender Melisa McNeil told reporters Thursday outside the courtroom where Cruz was charged that the 19-year-old has dealt with autism and depression and other psychological problems without the support system that most people have.

"He's sad. He's mournful. He's remorseful. He is fully aware of what is going on, and he's just a broken human being," she said.

Law enforcement sources told ABC News that Cruz said he heard voices in his head that gave him instructions for carrying out the attack. The sources described the voices as "demons."

Culture 'that embraces the dignity of life'

President Trump said in televised remarks from the White House Thursday morning that his administration is working closely with local authorities to investigate the shooting.

"We are committed to working with state and local leaders to help secure our schools, and tackle the difficult issue of mental health," he said.

"We must also work together to create a culture in our country that embraces the dignity of life, that creates deep and meaningful human connections and that turns classmates and colleagues into friends and neighbors."

As news of the shooting unfolded Wednesday, Sen. Chris Murphy, D-Conn., said on the Senate floor that Congress bears responsibility for the "epidemic of mass slaughter" in the country, noting it was the 18th school shooting this year.

"This epidemic of mass slaughter, this scourge of school shooting after school shooting," Murphy said, "it only happens here not because of coincidence, not because of bad luck, but as a consequence of our inaction. We are responsible for a level of mass atrocity that happens in this country with zero parallel anywhere else."

Murphy, who represents the state where the 2012 Sandy Hook Elementary School attack in which 20 children were fatally shot took place, said "this happens nowhere else other than the United States of America."

Dominic Rapini, a Republican challenger to Murphy in this fall's election, told WND he believes a focus on gun control distracts from "the root cause" of the problem, the breakdown of culture and family.

Noting Cruz's "professional school shooter" comment, Rapini said lawmakers "need to be talking about making sure that law enforcement has the tools to visit these kids and put them on the radar."

Rapini recalled that when he was in high school in Hamden, Connecticut, in the 1970s his school had a rifle range.

"Kids would routinely get on the bus with a .22 rifle and go to school. We didn't have mass shootings in the 1970s," he said.

"So, we have to ask ourselves, what else has been happening in the last 30 years?"

Pelosi: Gun control more important than election

Connecticut's senior senator, Democrat Richard Blumenthal, took issue with Trump's focus on mental health, pointing out the high rates of gun violence in the United States compared with other countries.

"The president is going to talk, but thoughts and prayers, words of consolation, talk about mental health are simply not enough. They must be followed by real action," he said in an interview with MSNBC. "The president has to lead or get out of the way."

House Minority Leader Nancy Pelosi, D-Calif., said Thursday that passing gun-control legislation is more important than the Democrats winning back the House in the fall.

Sen. Marco Rubio, R-Fla., said Thursday in a Senate floor speech that passing laws won't necessarily stop mass shootings like the one that took place in his state Wednesday.

"I'm trying to be clear and honest here, if someone's decided I'm going to commit this crime, they will find a way to get the gun to do it," Rubio said. "That doesn't mean you shouldn't have a law to make it harder; it just means understand, to be honest, it isn't going to stop this from happening."