Police arrested a man at Atlanta’s bustling airport on Monday after getting a tip from his family that he was planning to shoot up the place – and found an assault rifle and ammunition in his truck outside, the city’s police chief said.

Billy Joe Cagle, of Cartersville, Georgia, had described his plan to shoot up the world’s busiest airport on a social media livestream, said Darin Schierbaum, the chief of police, during a news conference.

“The Cartersville police department was alerted by the family of Mr Cagle that he was streaming on social media that he was headed to the Atlanta airport, in their words, to ‘shoot it up,’ and the family stated that he was in possession of an assault rifle,” Schierbaum said.

Cagle, 49, arrived at Hartsfield-Jackson Atlanta international airport in a Chevrolet pickup truck that was parked right outside the doors to the airport terminal. When police went to the vehicle, they found an AR-15 with 27 rounds of ammunition, Schierbaum said.

“We’re here today briefing you on a success and not a tragedy because a family saw something and said something,” the chief said.

Greg Sparacio, the Cartersville police captain whose department received the initial tip from family members, said Cagle “had the intention to inflict harm to as many people as he could”.

During the news conference, police showed surveillance video that shows Cagle arriving at the airport and officers’ body-worn camera video of his arrest.

A Chevrolet flatbed pickup truck is seen arriving curbside at the airport terminal around 9.30am, and then a man police identified as Cagle is seen entering the airport a few minutes later. He walks over to the Transportation Security Administration security checkpoint and had “high interest in that area”, Schierbaum said.

Body-camera footage shows Atlanta police officers, who had a photo of Cagle provided by his family on their phones, approach him and start asking him questions before taking him into custody. As they take him to the ground and put handcuffs on him, Cagle can be heard yelling.

Cagle has been charged with making terroristic threats, criminal attempt to commit aggravated assault, possession of a firearm during the commission of a felony and possession of a firearm by a previously convicted felon, Schierbaum said.

Cagle was booked into the Clayton county detention facility on Monday evening, according to online jail records. Attempts to reach his family and co-workers through multiple phone numbers and emails were unsuccessful. It wasn’t immediately clear whether he had a lawyer who could comment on the charges.

Nick Roberts, who has known Cagle since high school, texted his friend Sunday night after being concerned by Facebook posts he had made. He said Cagle was struggling with mental health issues. Cagle had posted on Facebook earlier Sunday that he is schizophrenic and was taking medication.

Roberts said Cagle called him at about 9pm Sunday night and assured him he was OK. Roberts said Cagle loved his two daughters and worked hard hauling hay and doing fencing work.

“I want folks to know that he wasn’t some monster,” Roberts said. “This was a very big surprise for a lot of us that went to high school with him and know him in the community.”

Atlanta police will work with federal authorities to determine how he obtained the gun, “which he was not able to legally possess”, Schierbaum said.

Andre Dickens, the mayor of Atlanta, said “we’re thankful to God” that a tragedy was averted.

“We’re thankful to God and to good information, and good intel, and good people for this crisis being averted,” Dickens said.

Kristi Noem, the US homeland security secretary, said in a post on the social platform X: “I am thankful this individual was taken into custody by law enforcement before harming anyone.”