The county sheriff in charge of investigating the mass school shooting in Parkland, Florida, pleaded with lawmakers on Thursday to give police and doctors more power to involuntarily hospitalize people for psychiatric evaluation over violent and threatening social media posts.

The sheriff, Scott Israel, of Broward County, described the accused shooter's social media posts as "very disturbing" at a news conference and asked state and federal legislators to expand the state's Baker Act, which says a person can be detained against their will for up to 72 hours under certain circumstances.

The accused, Nikolas Cruz, 19, has confessed to the shooting at Marjory Stoneman Douglas High School on Wednesday, authorities said. He has been charged with 17 counts of premeditated murder.

Israel said the Baker Act allows law enforcement or medical professionals to confine a person involuntarily, "but you have to have a reason, you have to be able to articulate that they're a threat to themselves or a threat to someone else."

Israel pleaded with lawmakers in Tallahassee, the state capital, and Washington to give police the power to detain people "if they see something on social media, if they see graphic pictures of rifles and blood and gore and guns and bombs, if they see something, horrific language, if they see a person talking about ‘I want to grow up to be a serial killer.'"

"People are going to be rightfully so concerned about their rights, as am I, but what about the rights of these students?" the sheriff said. “What about the rights of young kids who go to schools with book bags and pencils? Don't they have the right to be protected by the United States government to the best of our ability?"

Attorney General Jeff Sessions echoed the need for allowing law enforcement to intervene in certain circumstances in an interview with right-wing site Breitbart News.

Related: FBI was alerted about school shooting threat on YouTube

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"All of law enforcement is deeply concerned about this trend of violence in schools and other, similar places," he said.

A police officer comforts a woman. Giorgio Viera / EPA

"I was with the Major County Sheriffs' Association this morning, and they all said, and believe, that there are signals and signs before these shootings that, if recognized, could lead to intervention, and could stop these events from occurring," Sessions said.

Annette Christy, director of the Baker Act Reporting Center, which collects and analyses data on involuntary hospitalizations in the state, said there usually has to be "evidence of harm, self-harm or harm to others, or self-neglect and evidence of mental illness."

Christy, an associate professor at the University of South Florida, said, however, that people with mental illness have a right to live their lives and that’s why the “harm criteria are important.”

"When it crosses a line — when somebody is a harm to themselves so others — their civil liberties can be taken away to protect themselves and protect people in the public," she said.

A 2017 report on the Baker Act by the center found that there were 194,354 involuntary examinations in fiscal year 2015-16, a 3.4 percent increase from the prior fiscal years and a 33.8 percent increase from fiscal year 2010-11. About half of the involuntary exams were initiated by law enforcement, according to the report.

Mourners react during a community prayer vigil for victims of yesterday's shooting at nearby Marjory Stoneman Douglas High School in Parkland, at Parkridge Church on Feb. 15 in Pompano Beach, Florida. Jonathan Drake / Reuters

Christy said that there was currently no language in the law regarding disturbing social media posts or images and that specific situations that can lead to a Baker Act exam "out in the real world can vary quite a bit."

She added that while she understood the point of Israel's request, "that’s widening the net way wide."

"We need to develop prevention and alternatives for law enforcement so they don’t have to bring youths in," she said. "I really get it, but we need to think of these other possibilities, because the goal is you don’t want to end up that things get so bad that he has to have a Baker Act exam."

She also noted that "Florida is a very poorly funded state in terms of mental health."

Israel in an appearance on MSNBC Thursday night said he was not calling for law enforcement to become involved just because someone posts a photo of a weapon.

"I'm talking about being around bombs, possibly talking about ‘I want to be a serial killer,’ talking about taking people’s lives,” Israel said. "Just taking a picture with a gun or a knife or a weapon — that in and of itself is clearly not even remotely something that we’re concerned about."

He said that "we need to do things differently" and empower police to help get people who need mental health treatment help.

"I feel strongly about that. And everybody has their opinion, but I have mine, and I don't know how many people with their opinions went into a school yesterday and saw 17 dead people," Israel said.

Cruz was expelled from the school where the shooting took place, and one former classmate said he sometimes posted pictures of "dead lizards and stuff that he shot" on his Instagram feed.

Additionally, a YouTube user who used the same name as Cruz was investigated by the FBI for a comment boasting about plans to shoot up a school last September, the agency said.

The FBI was alerted to the comment but failed to identify the user, said Robert Lasky, the FBI agent in charge of the Miami division. The comment did not include information about timing or location, Lasky said at a news conference.