Virginia State Police tried to pull over Vester Flanagan, known on air as Bryce Williams, around 11:30 a.m., but he sped away. Minutes later, he ran off the road and crashed. As troopers approached the car, they saw that the driver had suffered a gunshot wound. He was taken to a hospital for treatment.

A televised attack on reporter Alison Parker and cameraman Adam Ward was broadcast live on WDBJ around 6:45 a.m. as they interviewed Vicki Gardner, a local chamber of commerce director, about an event at a lake near Moneta. The report was supposed to be a light morning show feature.

Shots were heard, and Ward's camera fell to the ground. Parker screamed over and over as the shots rang out. The station cut away to a shocked news anchor.

The video showed a glimpse of a man who appeared to point a gun toward the downed cameraman.

Gardner was shot in the back and was, as of mid-morning, in surgery, one of her colleagues told CNN.

As the station wrestled on air with remembering the slain newswoman, who was just 24 years old, and the cameraman, who was 27, law enforcement said they were looking for a person who used to work at WDBJ.

Flanagan was driving a gray 2009 Mustang, said a representative of the Augusta County Sheriff's Department in Virginia. According to a former station employee, Flanagan worked at WDBJ as a reporter for about a year. The former employee said Flanagan was fired from the station, though the reason for the firing was not made public.

Shocking posts of the slayings

Two videos posted late Wednesday morning on a Twitter account under the name Bryce Williams showed someone walking up to the WDBJ news crew and pointing a gun. One of the videos shows the gun firing.

Another tweet said, "I filmed the shooting." The same two videos -- playing together in one post -- appeared on a Facebook page under the same name. Minutes after these videos appeared, the Twitter account was inaccessible; a message on the page said the account was suspended.

Authorities had said the gunman may be a disgruntled WDBJ employee, Virginia Gov. Terry McAuliffe said Wednesday in a live interview with WTOP radio. He said that police were pursuing the suspect and that they hoped to have him in custody soon. McAuliffe said authorities know who the suspect is.

They were working with a name and license plate number for a person believed to be the shooter, according to a law enforcement official.

The gunman is believed to have fired six or seven times, WDBJ General Manager Jeff Marks said.

Matthew Horace, a former executive with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, told CNN that it's likely that footage from closed-circuit security cameras around Bridgewater Plaza, where the shooting happened, are helping investigators identify the shooter and the kind of vehicle that person might have been driving.

Judging by the eight shots he heard in the video, Horace said, the shooter probably used a semiautomatic pistol.

CNN's Pamela Brown, Evan Perez and Marylynn Ryan contributed to this report.