Flanagan was hired by WDBJ7, in Roanoke, Virginia, in March 2012 and was known on air by his professional name, Bryce Williams but within a few weeks, colleagues were complaining of "feeling threatened or uncomfortable" while working with him.
Internal memos from Dan Dennison, then news chief of WDBJ7, show concerns about Vester Flanagan's "aggressive" behaviour towards colleagues and indicated that the station tried to help him before firing him in February 2013. The memos highlight "heated confrontations" with camera operators and producers in front of guests while out covering stories.
Flanagan shot dead Alison Parker and Adam Ward at a shopping centre in Moneta on Wednesday. He however still had the effrontery to film the attack and then post it on social media. Our source claimed that it received a rambling fax from the 41-year-old describing himself as a "human powder keg".
The White House said Wednesday's attack showed the need for better gun control.
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.
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".
"Our thoughts and prayers at this time are with the victim's families and with WDBJ television station family," the statement added.
