Internal memos from Dan Dennison, then news chief of WDBJ7, show concerns about Vester Flanagan’s “aggressive” behaviour towards colleagues.
They indicate the station tried to help him before firing him in February 2013.
Flanagan shot dead Alison Parker and Adam Ward at a shopping centre in Moneta on Wednesday.
He filmed the attack and posted it on social media. ABC News also said it had received a rambling fax from the 41-year-old describing himself as a “human powder keg”.
The White House said the attack showed the need for better gun control.
Colleagues at WDBJ7, in Roanoke, Virginia, held a moment of silence at 06:45 (10:45 GMT) on Thursday – 24 hours on from the exact moment the reporter and cameraman were shot dead.
“Joining hands here on the desk,” said anchor Kim McBroom. “It’s the only way to do it.”
Flanagan was hired by WDBJ7 in March 2012 and was known on air by his professional name, Bryce Williams.
Within a few weeks, colleagues were complaining of “feeling threatened or uncomfortable” while working with him.
The memos highlight “heated confrontations” with camera operators and producers in front of guests while out covering stories.
By July 2012, Mr Dennison was requiring him to contact the Health Advocate, the employee assistance programme, or face being sacked.
“We can no longer afford to have you engage in behaviours that constitute creation of a hostile work environment,” he said.
Aged 24, was a reporter for WDBJ7’s Mornin’ show
Grew up in Martinsville, Virginia and edited her university newspaper
Joined WDBJ7 after internship and said she grew up watching the station
Was dating station anchor Chris Hurst
Aged 27, was a cameraman for WDBJ7
Went to school in Salem, Virginia, and graduated from Virginia Tech
Described by his employer as committed and a “fine photojournalist”
Was engaged to station producer Melissa Ott
Speaking on Wednesday from Hawaii where he now works, Mr Dennison said Flanagan had complained of racial discrimination but “all these allegations were deemed to be unfounded”.
He said when Flanagan was fired, he had to be escorted from the building by police “because he was not going to leave willingly or under his own free will”.
In the 23-page fax to ABC News apparently sent by Flanagan under his professional name, he complained of suffering discrimination and bullying at work for being gay and black.
He said his anger had been “building steadily” and that he had become a “human powder keg” that was “waiting to go BOOM!!!!”
The writer expressed admiration for the teenagers who killed 13 people at Columbine High School in Colorado in 1999 and said the attack in Charleston, South Carolina, in which nine black churchgoers were killed in June this year, was what “sent me over the top”.
Late on Wednesday, a representative for Flanagan’s family issued a statement expressing their “deepest condolences to the families of Alison Parker and Adam Ward”.
Alison Parker’s father said his family had lost their “bright, shining light”.
Ms Parker was conducting a live interview with a guest on tourism for the breakfast show, filmed by Mr Ward, when the incident occurred.
Suddenly, shots rang out, and viewers saw the camera fall to the ground. Screams could be heard and the footage captured a brief glimpse of the gunman.
The station cut back to the studio – journalists would later have to continue broadcasting on the deaths of two of their colleagues.
Hours later, the gunman posted footage online of himself opening fire at close range. This was later removed.
He killed himself after a police chase.
The interviewee, Vicki Gardner of the Smith Mountain Lake Regional Chamber of Commerce, is in a stable condition in hospital following surgery.
President Barack Obama repeated his call for tougher gun laws after the attack.
“We’re willing to spend trillions of dollars to prevent terrorist activities, but we haven’t been willing so far at least to impose some common sense gun safety measures,” he said.
However Republican presidential hopefuls Jim Gilmore and Ben Carson warned against any rush to introduce tougher gun controls.
“We’re not going to let this madman take away the lawful rights of Americans to keep and bear arms,” Jim Gilmore, a former governor of Virginia, told CNN.