LOS ANGELES — At Los Angeles International Airport last spring, a dispatcher received an anonymous call suggesting that a Spirit Airlines flight to Las Vegas was "going to blow up."

In April, an employee at a legal clinic received a phone call from someone threatening to bring a grenade to the office if they didn't receive a callback from an attorney.

And then in early October, someone reported a bomb was inside L.A. City Hall.

All were serious threats fielded by the Los Angeles Police Department in the last year and a half. And all, as follow up investigations would reveal, were made up. What separated the City Hall case from the other two is that authorities have said they are investigating Brian Williams, a top deputy to Mayor Karen Bass, on suspicion of making the false claim.

The revelation brought a range of responses, from the requisite internet snark — "Maybe he had a test that he hadn't studied for?" — to open-mouthed shock of City Hall and LAPD staffers who said in private conversations that the allegations didn't square with the man they knew.

Law enforcement experts say such threats are common and tend to ramp up around major social events, such as a national election. Other spikes in reports of suspicious bags or items happen in the wake of a major incident, such as the 1995 Oklahoma City bombing, when authorities were inundated by reports from the newly vigilant public.

Even if the reports appear to be a hoax at first glance, authorities say they can't take chances and have to investigate each one, which involves clearing a building and bringing in explosive-sniffing dogs.

LAPD records show the department has investigated scores of bomb threats at government offices, schools and sports arenas, including at least 144 cases in which police found an explosive device. Last year, there were 34 such cases, tied for the highest number in at least five years.

With the growth of privacy-focused technology and social media, identifying the source of the threat can be difficult.

On Thursday, a day after the Williams news broke, the air was festive at City Hall, where a long line of people waited to take pictures with the mayor in front of a towering Christmas tree in the rotunda. But behind closed doors, many government staffers continued to speculate about the allegations against Williams.

Questions remain about when LAPD investigators first began to suspect Williams may have been involved, and when they informed department leaders and Bass' office of the investigation. An attorney for Williams said that he was innocent and "intends to vigorously fight the allegations.

According to two sources familiar with the allegations, who requested anonymity because they were not authorized to speak publicly about the ongoing investigation, the supposed bomb threat was made sometime in the first week of October.

As is typically the case in federal probes, authorities have been tight-lipped, with an FBI spokesperson declining to comment.

Federal agents searched Williams' home Tuesday, according to a statement issued by a spokesperson for Bass.

In a separate statement, the LAPD identified Williams as the "likely" source of the threat.

Williams has been placed on administrative leave pending the outcome of the investigation.

"Importantly, he has not been arrested, nor charged, and will continue cooperating with the investigation through his attorneys," Williams' attorney Dmitry Gorin said.

If true, the allegations would mark a stunning turn for a widely liked public official, who was described by several people in city government as soft-spoken, a dapper dresser and a co-worker who had never shown anger or impulsive behavior on the job.

Williams has held a variety of government positions spanning more than three decades.

He has spent nearly two years as a deputy mayor in Bass' office, working on issues ranging from police hiring to public safety spending. He was also among the mayor's trusted inner circle during the months-long search for a police chief that ended with the appointment of Jim McDonnell in early October.

Williams was a deputy mayor in the administration of Mayor James K. Hahn, who held office from 2001 to 2005. Before that, he spent several years an assistant city attorney in Los Angeles.

From 2016 to 2023, Williams was the executive director of the Sheriff's Civilian Oversight Commission, according to his LinkedIn page. Working in Bass' office, Williams oversaw the Police Department, the Fire Department, Port Police, Airport Police and the city's emergency management agency, according to his hiring announcement.

In that role, Williams was a regular presence at police graduations, news conferences, community meetings and other events across the city, often wearing a well-pressed suit and a bowtie. When Dist. Atty. Nathan Hochman was sworn in this month, Williams was the city official chosen to address the audience on behalf of the mayor.

Some in the city's Black political and religious establishment have rallied behind Williams, issuing statements of support and disbelief. A rally for supporters is planned for Friday morning outside the 77th Division police station in South L.A.

Most bomb threat cases are handled by the Major Crime Division's Criminal Conspiracy Section, which also investigates bombings, complex arsons and suspects found in possession of bomb-making materials.

Over the past several years, investigators from the unit have sought search warrants for access to the phone and email records, trying to get to the bottom of bomb threats, usually seeking suspects who have tried to mask their identities.

In one such case, Major Crimes detectives began investigating after someone on the social media platform X posted that a bomb had been placed on the 45th floor of a downtown high rise and tagged the LAPD's account. The office houses the Lewis-Brisbois law firm.

A similar threat was made to the Inner-City Law Center a month or so prior, in which someone faxed the firm demanding that if a particular employee did "not call this number back by the end of the day we are taking a grenade to inner city law GET ON IT ASAP."

Major Crimes detectives authored a search warrant for the social media user who reportedly made the post, which revealed the Gmail address registered to that account.

In the LAX case last year, police said a dispatcher received an anonymous phone call saying that a "The flight to Las Vegas at 1045 Spirit Airlines 56 B gate is going to blow up." The dispatcher reported the call to Airport Police, which searched the area and didn't find anything.

Major Crimes detectives determined that the call had been placed through TextNow, an app that offers users the ability to text and call anonymously, and they asked the company to turn over information about the subscriber.

The vast majority of bomb threat cases go unsolved, according to officials.

Simon Osamoh, founder of Kingswood Security, a risk management consulting firm from Minneapolis, said police are increasingly responding to hoax bomb threats and so-called swattings, in which individuals make false 911 calls in order to induce an armed law enforcement response.

The LAPD's response to such incidents at the homes of public figures has come under scrutiny in recent years, including a 2020 case at the home of a Black Lives Matter leader where the department was criticized for its aggressive response.

But in a nation where mass shootings have become tragically common, Osamoh said, police tend to take no chances.

"In the modern society where we live, it's very hard for them to take a conservative approach," Osamoh said.

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