(Alan Diaz/AP)

Details were scant, but the similarities were unnerving.

Shots fired at the local Walmart. Terrified shoppers running for cover. Frantic calls streaming into 911. The Baton Rouge store is nearly 1,000 miles east of the El Paso Walmart where, just 72 hours earlier, comparable initial reports gave way to scenes of chaos and mass violence: 22 dead and many more injured.

In the Louisiana capital, training took over. Law enforcement responded en masse. Officers from the East Baton Rouge Sheriff’s Department were on the scene in four minutes, then city and state police, with agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives. They swarmed the Walmart.

But soon after wading into the bedlam, authorities discovered there was no “active shooter.” No gunman stalking the store halls and firing wildly like the suspect in El Paso. Instead, relieved officers encountered a decidedly different challenge: policing in the days after high-profile mass shootings in Gilroy, Calif., El Paso and Dayton that left people deeply anxious.

“Thank God we didn’t need all those individuals, but I’m glad they responded,” East Baton Rouge Sheriff Sid Gautreaux said at a Tuesday news conference. “Because, as you all know, something as tragic as what took place in Dayton or El Paso could happen anywhere, anytime.”

The urgent response was prompted by two men fighting, one of whom threatened to stab the other with a pair of scissors, police told local media. The second man pulled his gun and pointed it at the scissor-wielding man, which police said was an act of self-defense. The sight of a gun sent bystanders into a panic, rightfully so, and witnesses would later report they heard “popping” noises.

As of Wednesday, the investigation led law enforcement to two suspects, according to the Advocate: Robert Tucker and Jacob Bess. Tucker, 44, was arrested for aggravated assault with a firearm, and, Bess, 32, was issued misdemeanor summons for disturbing the peace.

“The national climate regarding these incidents has the nation on edge, and citizens’ anxiety levels much higher than normal,” the sheriff’s department added in a written statement.

Anxiety after shootings can feed shocking — but unverified — social media reports, creating a frenzied information ecosystem that could itself be a threat to public safety, experts say. This week, that ecosystem is thriving.

The aftermath of an attack is an especially intense time for first responders, said Frank Straub, the director of the Center for Mass Violence Response Studies at the nonprofit Police Foundation.

“Everybody is amped up,” Straub told The Washington Post. “These calls come in and the officers are going. They have to respond — you have to take every threat seriously — so it becomes a drain on law enforcement resources and becomes a drain on officers themselves.”

False or misguided 911 calls are often well-intentioned, he said, but they can be based on flowcharts of unreliable rumor. It can start with a shred of information, something only half-true that gets shared and re-shared online. If it gets enough attention, Straub said, a news organization eager to be first to the story will report it, lending it a sheen of credibility. From there, the narrative is obdurate.

“You see some of these social media posts take on a life of their own and they become the truth,” Straub said. “Now we have this bad information coming into police dispatchers and it’s being reinforced on the news, and it’s an added burden of trying to figure out what’s fact and what’s fiction.”

In Cambridge on Tuesday, the search for a homicide suspect unfolded in a similar fashion.

Harvard University police warned students that a man wanted for a killing in Philadelphia could be hiding out in Harvard Square. They said the man might be armed. After Cambridge police searched the square, rumors of an “active” gunman blossomed on social media, which authorities believe were driven in part by people with no connection to the Cambridge area.

“You’ve got people driving misinformation that are not from this community, and creating potential hysteria when they don’t even know our community,” said Jeremy Warnick, a Cambridge Police spokesman.

Cambridge officers arrested the Philadelphia suspect that day, and they provided frequent updates on social media in order to fight misinformation — a tactic the department honed in the days after the 2013 Boston Marathon bombing.

In a separate incident in New York, crowds in Times Square scattered when motorcycles backfired, a quotidian city sound.

“There is no #ActiveShooter in #TimesSquare,” an NYPD precinct wrote on Twitter after reports of a “running mob” in the jam-packed tourist spot. “Motorcycles backfiring while passing through sounded like gun shots. We are receiving multiple 911 calls. Please don’t panic. The Times Square area is very safe!”

In Long Beach on Monday, however, online reports actually led to the capture of a man who was reportedly directing violent threats at a rally for Democratic presidential candidate Sen. Bernie Sanders (Vt.), who spoke there on Tuesday. In a statement announcing the man’s arrest, Long Beach police vowed extra patrols and an increased presence at events and high traffic public places following the threats and the shootings in El Paso and Dayton.

A commitment to community policing, especially after traumatic national events, Straub said, can help prevent future attacks. If there’s a shooting at a school or a church somewhere in the country, departments elsewhere may increase visibility at their local institutions. It serves a dual purpose, he said: trust building and information gathering. And even though false alarms can be taxing, Straub said authorities would rather know about something and investigate it than wish they had.

Read more:

Two cities united in a tragedy uniquely American

The lives lost in El Paso

The lives lost in Dayton