Devin Kelley, 26, had just exited the First Baptist Church where he had shot and killed 26 worshipers with an assault rifle and was headed for his Ford Explorer, which had a door open and the engine running.
According to the authorities, a neighbor who lived across the street had grabbed his own AR-15 rifle and was exchanging shots with Kelley.
That's when Langendorff drove up in his pickup truck.
"I pulled up to the intersection," the lanky Texan with a cowboy hat and a longhorn skull tattoo on his neck, told CNN.
"Right whenever I pulled up I saw the shooter coming out about where the cars were parked and the other gentleman coming from across the street," he said.
"Both had weapons drawn and in a matter of half a second there was exchange of gunfire," he said. "It lasted just a few seconds.
"And the shooter got in his vehicle and took off," he said.
"And the gentleman with the rifle came across the street opened my door and said 'He just shot up the church and we got to chase him,'" Langendorff said.
"And I said 'Let's go.'"
"That's what you do," he said. "You chase the bad guy."
According to officials, the barefoot man, identified in media reports as a plumber named Stephen Willeford, wounded Kelley before he took off in his car with Langendorff in pursuit.
Langendorff told CNN he reached speeds of up to 95 miles per hour (150 kilometers per hour) as he and the other man chased Kelley.
"We didn't even stop at this intersection," Langendorff said. "We buzzed right on through.
"And I had to catch the guy. I had to make sure he was caught."
Langendorff estimated that the chase lasted about 10 to 12 minutes and he was on the phone with police dispatchers throughout, telling him where they were.
"At one point the gentleman riding with me said, 'you may have to use your truck to get him off the road,'" he said.
"And there was no hesitation -- it was, you know, do everything necessary to make sure that this guy is stopped."
Langendorff said the chase "ended up with him wrecking his vehicle into the ditch."
"The other gentleman got out immediately and drew his rifle on him and he was telling him 'Get out, get out,' and the shooter never got out," he said.
"We barricaded behind my truck until police showed up."
Langendorff praised the actions of the other man saying he's "very much a hero.
"He did absolutely the right thing which is try to take him down on the scene," he said. "From what I know he was just taking a nap and heard the gunshots and reacted.
"He was barefooted. He had no shoes on or nothing but he was ready to act," he told CNN. "He did all the right things."
According to officials, Kelley's rampage at the church may have stemmed from a conflict with his mother-in-law, who prayed at that church but was not present at the time of the shooting.
They said Kelley, who was court-martialed and received a bad conduct discharge from the Air Force three years ago, died of a self-inflicted gunshot wound.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
Get the latest election news, live updates and election schedule for Lok Sabha Elections 2019 on ndtv.com/elections. Like us on Facebook or follow us on Twitter and Instagram for updates from each of the 543 parliamentary seats for the 2019 Indian general elections.