(CNN) Some are teenagers accused of threatening to gun down classmates. Others allegedly issued social media warnings of attacks on store customers or coworkers. Still others are said to have vowed to unleash small arsenals against victims based on their race or religion.

More than two dozen people have been arrested over threats to commit mass shootings in the weeks since 31 people were killed in one August weekend in shootings in El Paso, Texas, and Dayton, Ohio,

The raft of cases follows a directive by the FBI director immediately after those two massacres for agency offices nationwide to conduct a new threat assessment in an effort to thwart more mass attacks.

The FBI was concerned that US-based domestic violent extremists could become inspired by the attacks to "engage in similar acts of violence," the agency said in a statement.

At least one person now facing charges told deputies he simply wasn't being serious, they said. Joke or not, though, such comments in many places are a felony.

"After the mass violence we've seen in Florida and across the country, law enforcement officers have a responsibility to investigate and charge those who choose to make these types of threatening statements," the sheriff's office involved in that case wrote on its Facebook page.

Here are the known threats with publicized arrests that law enforcement agencies have investigated since the Dayton and El Paso shootings:

August 4: A man from the Tampa area called a Walmart and told an employee he would shoot up the store, the Hillsborough County Sheriff's Office said in a statement. The man faces a false threat charge.

August 7: Police in Weslaco, Texas, arrested a 13-year-old boy. The boy will face a charge of terroristic threat for making a social media post that prompted a Walmart to be evacuated, police said on Facebook. The boy's mother brought him to the station.

August 8: A man is accused of walking into a Walmart in Missouri equipped with body armor, a handgun and a rifle less than a week after a gunman killed 22 people in a Texas Walmart A man is accused of walking into a Walmart in Missouri equipped with body armor, a handgun and a rifle less than a week after a gunman killed 22 people in a Texas Walmart says it was a "social experiment" and not intended to cause panic. The 20-year-old was charged with making a terrorist threat.

August 9: A 23-year-old Las Vegas man is charged with possessing destructive devices after authorities found bomb-making materials at his home. The FBI says he was A 23-year-old Las Vegas man is charged with possessing destructive devices after authorities found bomb-making materials at his home. The FBI says he was planning to attack a synagogue and a gay bar

August 9: A 26-year-old Winter Park, Florida, man was arrested after investigators say he posted a threat on Facebook that he was about to have his gun returned and people should stay away from Walmart.

August 10: Officers responded to a threat a man posted on social media, the Harlingen, Texas, Police Department said in a statement. A man was Officers responded to a threat a man posted on social media, the Harlingen, Texas, Police Department said in a statement. A man was arrested at his home on charges of making a terroristic threat.

August 11: A Palm Beach County, Florida, mother is accused of threatening to carry out a shooting at an elementary school because her children were being moved there, according to A Palm Beach County, Florida, mother is accused of threatening to carry out a shooting at an elementary school because her children were being moved there, according to CNN affiliate WFTS . The 28-year-old woman is charged with sending a written threat to commit bodily injury.

August 11: A Mississippi teen is accused of making threats in the Lamar County School District, A Mississippi teen is accused of making threats in the Lamar County School District, the agency says on Facebook

August 12: Authorities charged an 18-year-old Ohio man who the FBI says Authorities charged an 18-year-old Ohio man who the FBI says threatened to assault federal law enforcement officers and showed support for mass shootings in a post online. Court documents say that the teen had a stockpile of weapons and ammunition.

August 12: A 25-year-old Jefferson County, West Virginia, man was arrested on charges of making terroristic threats online to kill people, according to CNN affiliate A 25-year-old Jefferson County, West Virginia, man was arrested on charges of making terroristic threats online to kill people, according to CNN affiliate WDVM

August 13: arrested and charged a 15-year-old Minnesota girl for threatening a school shooting on social media. Albert Lea Police arrested and charged a 15-year-old Minnesota girl for threatening a school shooting on social media.

August 13: A man was arrested in Phoenix after police say he threatened to blow up an Army recruitment center, according to CNN affiliate A man was arrested in Phoenix after police say he threatened to blow up an Army recruitment center, according to CNN affiliate KTVK

August 15: A tip from a citizen led Connecticut authorities and the FBI to investigate and arrest a man who they said expressed an interest in committing a mass shooting on Facebook and had weapons and tactical gear, A tip from a citizen led Connecticut authorities and the FBI to investigate and arrest a man who they said expressed an interest in committing a mass shooting on Facebook and had weapons and tactical gear, the FBI and Norwalk Police Department said.

August 15: A 15-year-old girl was arrested in Fresno, California, for : A 15-year-old girl was arrested in Fresno, California, for posting a photo of a Walmart gun case with rifles displayed and the caption, "Don't come to school tomorrow," the city's police chief said. "The teen's very bright future is now stained by this," he said, adding she was booked with making terrorist threats.

August 16: A 15-year-old boy was A 15-year-old boy was taken into police custody in Volusia County, Florida, after investigators say he threatened to commit a school shooting in comments on a video game chat platform.

August 16: Two Mississippi juveniles were arrested in connection with threatening messages to two Tupelo schools, placing a school in partial lockdown, according to CNN affiliate Two Mississippi juveniles were arrested in connection with threatening messages to two Tupelo schools, placing a school in partial lockdown, according to CNN affiliate WTVA.

August 16: A Florida man was A Florida man was arrested and charged with threatening to commit a mass shooting after his ex-girlfriend alerted authorities to a series of ominous text messages he sent her.

August 16: A 14-year-old in Arizona was arrested by Tempe Police after online threats were made against a school, according to CNN affiliate A 14-year-old in Arizona was arrested by Tempe Police after online threats were made against a school, according to CNN affiliate KNXV

August 16: A Chicago man, 19, was A Chicago man, 19, was arrested after police say he threatened to kill people at a women's reproductive health clinic on iFunny, a social media platform where users can post memes, federal prosecutors said Monday.

August 16: A 35-year-old Clarksburg, Maryland, resident was arrested in Seattle after being charged with threatening to kill people and calling for the "extermination" of Hispanics, according to A 35-year-old Clarksburg, Maryland, resident was arrested in Seattle after being charged with threatening to kill people and calling for the "extermination" of Hispanics, according to a statement released by the US attorney for the Southern District of Florida.

August 17: New Middletown Police arrested a self-described white nationalist who they say threatened to New Middletown Police arrested a self-described white nationalist who they say threatened to shoot an Ohio Jewish community center

August 18: A man was arrested in Reed City, Michigan, after authorities said he posted online videos making threats toward Ferris State University and other locations, according to CNN affiliate A man was arrested in Reed City, Michigan, after authorities said he posted online videos making threats toward Ferris State University and other locations, according to CNN affiliate WXMI

August 18: Claremore, Oklahoma, police arrested an 18-year-old who they say made social media threats against police officer families, according to Claremore, Oklahoma, police arrested an 18-year-old who they say made social media threats against police officer families, according to a Facebook post from the Claremore Police Department

August 19: A 38-year-old truck driver was arrested after making "credible threats to conduct a mass shooting and suicide" planned for Thursday, an FBI special agent said in a sworn affidavit filed in the Southern District of Alabama.

August 19: Maui Police arrested an 18-year-old man after a social media post claimed he intended to "shoot up a school," according to CNN affiliate Maui Police arrested an 18-year-old man after a social media post claimed he intended to "shoot up a school," according to CNN affiliate KITV.

August 19: A 37-year-old Rapid City, South Dakota, man was arrested and charged with threatening to blow up state and federal government agencies, Pennington County Sheriff's Office said in a post on A 37-year-old Rapid City, South Dakota, man was arrested and charged with threatening to blow up state and federal government agencies, Pennington County Sheriff's Office said in a post on Facebook.