Cowell's company, Syco, told the Herald's Diary: "We have latterly been made aware of the situation and take this matter very seriously. We are currently looking into it with the local producer MediaWorks."
Brider was sentenced to eight years' jail for his part in the manslaughter of 16-year-old Jeremy Frew in Wanganui in 2004, and in a segment aired on X Factor this week admitted on air that he was involved in a fatal stabbing and described the crime as "a commotion".
However, the victim's mother says Brider did not tell the whole truth in the segment and lashed out at TV3 for not warning her of Brider's appearance.
The producers of The X Factor NZ, MediaWorks, said yesterday that it would be airing a public apology to Jeremy Frew's family on forthcoming episodes of the show.
A clause in the contract held by Syco Entertainment and FremantleMedia stipulates the show can't be brought into disrepute in accordance with the third-party license agreement. It is understood that special dispensation would have needed to be sought to use Brider, and MediaWorks failed to get permission.
READ EXCLUSIVE: Cowell takes dim view of killer's X Factor debut
Meanwhile it has been revealed Brider was banished from Wanganui by the Parole Board, and did not move to Masterton "out of respect" for his victim's family as he claimed on the show this week.
And a man Brider assaulted the same night he killed the 16-year-old has a message for the wannabe singer: "Don't ever bring up that tragic night's events again."
When Brider was released from prison after serving six years for the manslaughter of Jeremy Frew, 16, a number of conditions were imposed by the Parole Board, including not entering the Wanganui District.
On Tuesday's X Factor, Brider said he moved to Masterton after his release "out of respect" to his victim's family.
However, it was not Brider's decision to relocate. In January 2010 Brider was refused parole because he was considered to be an undue risk to the safety of the community. A year later the board agreed to release him, saying there was more virtue in his "getting back into the community as a law-abiding citizen" than keeping him behind bars. A condition of his parole was that he not enter the Wanganui district at any time.
The Herald has also learned that Brider twice spent time in prison in the two years before Mr Frew was killed.
Another potential hole in Brider's story was raised by his mother. On the show he spoke about his parents being "reasonably violent to each other and to me". His mother denied that claim in a social media post after the episode aired. "I didn't use [sic] 2 beat him up, the dreamer," she said.
Neither Brider nor his mother would comment.
Daniel Gray was assaulted by Brider and three others shortly before Mr Frew was stabbed to death. He felt Brider had "paid his dues" but was unimpressed by his television spiel.
"What was broadcast was not forthcoming of the actual events leading to Brider's convictions and incarceration. The details aired were an extremely dimmed-down version of events and was distasteful, to say the least ."
He did not want Brider to fail in life but asked that he be honest in future and respect his victims.
Jeremy Frew's mother, Donna Travers, said the issue was that incorrect and misleading information was broadcast about the case.
"I don't care what happens to Shae Brider ... everyone deserves a second chance. I care that my son's murder was raised again on national TV. My family has been destroyed over this, emotionally destroyed."
Jeremy's sister Jodie, who was watching The X Factor when Brider appeared, said his story was full of "half-truths" and minimised his involvement in her younger brother's death. "If you're going to own up to something like that, own all of it."
MediaWorks spokeswoman Rachel Lorimer said: "Our focus has been on communicating with the family of the victim and you will understand that out of respect for them, we have not made further comment while those conversations were taking place."
- Additional reporting Morgan Tait and Anna Leask
