A TV reporter and cameraman were shot to death on live television Wednesday by their former colleague, a journalist who also recorded himself carrying out the killings and then posted the video on social media.

The gunman, who was fired in 2013 from WDBJ in Roanoke, Virginia, fled the scene and went online, posting the video on Facebook and Twitter. He also reportedly faxed a 23-page manifesto and "suicide note" to ABC News, describing himself as a "human powder keg" that was "just waiting to go BOOM!!!!"

Vester Lee Flanagan II, 41, who appeared on WDBJ as Bryce Williams, had evidently been planning the attack for some time, authorities said. As he fled, he switched vehicles, picking up a rental car he had previously reserved at an airport. Troopers caught up with him hours later and hundreds of miles away after he fatally shot himself and ran off the road.

The live spot by reporter Alison Parker and cameraman Adam Ward was nothing out of the ordinary: They were interviewing a local official at an outdoor shopping mall for a tourism story. Then, at about 6:45 a.m., morning show viewers saw her suddenly scream and run, crying "Oh my God," as she fell. Ward fell, too, and the camera he had been holding on his shoulder captured a fleeting image of the suspect holding a handgun.

WDBJ quickly switched back to the anchor at the station, her eyes large and jaw dropping as she said, "OK, not sure what happened there." The station later went live again, reporting on their own staff as the story developed.

Parker and Ward died at the scene after the gunman fired about 15 shots. Their interview subject, Vicki Gardner, was in stable condition later Wednesday after surgery for her wounds.

Video posted on Bryce Williams' Twitter account and Facebook page hours later showed an outstretched arm holding the handgun. The shooter walked up to the victims and stood a few feet away, but with all three in the midst of the live TV interview, none seemed to notice. The gunman waited until Ward's camera was pointed at Parker, and then fired repeatedly.

Flanagan was described by Jeffrey Marks, WDBJ's president and general manager as an "an unhappy man" and "difficult to work with," always "looking out for people to say things he could take offense to."

"Eventually after many incidents of his anger coming to the fore, we dismissed him. He did not take that well," Marks explained, adding that police had to escort him out of the station when he was fired.

Ward, 27, was engaged to a producer at the station, Melissa Ott, who was celebrating her last day on the job. Parker, 24, had recently moved in with another co-worker, WDBJ anchor Christ Hurst.

Hurst wrote online that they hadn't shared their relationship publicly but "were very much in love." He said they had just moved in together and wanted to get married. "I am numb," he said.

Parker was raised in the Martinsville, Virginia, area and joined the station as an intern after attending James Madison University, where she was the editor of the school's newspaper, The Breeze.

Others at the station said it was particularly hard for Ott, who watched the shooting unfold from the control room.

"Adam was our go-to guy. He pretty much was available to do anything that we asked," said WDBJ spokesman Mike Morgan. "He did live shots during our morning show for several years."

Tweets posted on Williams' Twitter account Wednesday described workplace conflicts with both victims. They say Williams filed a complaint with the Equal Employment Opportunity Commission against Parker, and that Ward had reported Williams to human resources.

Marks said Williams alleged that other employees made racially tinged comments to him, but said his EEOC claim was dismissed and none of his allegations could be corroborated.

"We think they were fabricated," Marks said.

ABC News reported that a man claiming to be Williams called the network, saying he had just shot two people, and was faxing them a 23-page document. That document is being analyzed by investigators, Franklin County Sheriff W.Q. "Bill" Overton Jr. said at a news conference.

According to the network, the man claiming to be Flanagan says in the "suicide note" that he bought a gun two days after the Charleston, South Carolina church shootings, seeking revenge for racial discrimination, sexual harassment and workplace bullying he said he suffered as a gay black man.

"This gentleman was disturbed at the way things had turned out at some point in his life. Things were spiraling out of control," Overton said.

The shooting happened around 6:45 a.m. at Bridgewater Plaza in Franklin County, as Parker interviewed Gardner about the upcoming 50th anniversary festivities for Smith Mountain Lake, a local tourism destination.

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Ramsey reported from Charleston, West Virginia. Drew reported from Hardy, Virginia.

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This story has been corrected to show that Flanagan was fired from WDBJ in 2013, not this year.