MARKHAM, Virginia—Catching the Roanoke TV killer took 200 miles and 12 minutes.

Vester Lee Flanagan made it nearly to the rural town of Markham, Virginia—about 200 miles from where he gunned down two journalists on live television—before a slight Virginia state trooper figured out that the 2015 silver Chevrolet Sonic that had just zipped past belonged to the most wanted man in the state.

On Wednesday afternoon, state trooper Pamela Neff described what happened to a crowd of reporters gathered at a nearby abandoned rest stop across the interstate from where Flaganan’s car had crashed.

“The only thing that kicks in is our training,” Neff said. “You don’t have time to think about personal emotions. You only have time to think about what happens next.”

At 11:13 a.m., Flanagan tweeted from the road the first of two videos showing him opening fire on Alison Parker and Adam Ward earlier that morning. Police scanners at the time said they determined that Flanagan was using his phone.

At 11:18 a.m., Neff spotted Flanagan’s car but didn’t know yet that it belonged to him. At 11:20 a.m., radio squawked out Flanagan’s license plate number. Neff’s patrol car has a license-plate reader that scans every vehicle that passes it and stores the data for 24 hours. Once she entered Flanagan’s number, she got a hit—Flanagan was in that Chevy that had passed her three minutes earlier.

Neff took off after Flanagan and radioed for backup. Chasing the suspect brought a host of concerns: Neff said she didn’t want to pull him over close to one of the construction crews dotting that part of Interstate 66. When she did stop him, Neff wanted to have backup, given that he was presumed to be armed.

When Neff caught up with Flanagan, he was driving at the speed limit but straddling the center line of the road instead of staying in his lane. In the space of a few minutes, Flanagan’s car became the only civilian vehicle on the road—a half dozen cop cars closed were approaching from ahead and behind Flanagan.

When backup arrived, Neff fired up her lights and sirens, but Flanagan didn’t stop.

Instead, he kept on chugging down the middle of the road at a legal, even reasonable speed. Then, at 11:30 a.m., he veered off to the left and ran aground in the grassy median between the eastbound and westbound lanes.

Neff pulled up behind Flanagan, joined by other police. Officers found him suffering from a self-inflicted gunshot wound. At first he appeared to be dead, but then he registered a pulse and was treated for life-threatening injuries. Flanagan succumbed to those injuries around 1:30 p.m.

Neff didn’t answer questions about when Flanagan shot himself—whether he did so before or after veering off the road—and didn’t give any information about what cops found in his vehicle besides his body, gun, and the phone he used to show the world what he had done.