The transgender gunman behind Monday's horror shooting had a "vendetta" against his own family, his daughter has said.
Robert Dorgan, 56, who also used the name "Roberta Esposito", shot dead his 23-year-old son Aidan Dorgan and his ex-wife Rhonda, 52, in Pawtucket, Rhode Island.
Three other people were wounded in the attack and remain in critical condition at a local hospital.
Dorgan turned the weapon on himself after the rampage.
His daughter Amanda Wallace-Hubbard, 36, witnessed the shooting alongside her two young sons.
Authorities have confirmed the attack was targeted and arose from a family dispute.
Ms Wallace-Hubbard has now revealed her father harboured a "vendetta" against his own family, which she believes drove him to carry out the killings.
"I just want to make sure people understand this was one person's vendetta against their family," she told The Times.
Despite Dorgan being vocal online about his gender identity, his daughter insisted this was not what caused the family rift.
Aidan Dorgan, 23 (left) and his mother were killed by 'Roberta Esposito' (right) in Pawtucket on Monday | FACEBOOK
Robert Dorgan, 56, who also used the name 'Roberta Esposito', shot dead his 23-year-old son Aidan and his former wife Rhonda, 52
|"Gender identity was not remotely a factor in him being ostracized from the family, at least on the part of myself or my siblings, it really was just a symptom of something that had been going on that was much deeper his entire adult life," she told the New York Post.
The 36-year-old said her father 'struggled with demons' throughout his life.
She decided to distance herself from him after having children of her own.
Ms Wallace-Hubbard said she feared her sons would be next as her father continued shooting.
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PICTURED: Ava, Rhonda, Aidan and Colin Dorgan after Aidan's graduation | FACEBOOKA bystander named Michael Black intervened, leaping over seats to grab Dorgan's pistol and tackled him to the ground.
"Until that Good Samaritan incapacitated him, I really feared that my sons were next. I can't thank him enough - I'm certain my sons and I are alive because of him," Ms Wallace-Hubbard said.
Mr Black suffered a hand injury and a facial burn from an ejected shell casing during the struggle.
After several people restrained Dorgan, he pulled out a second pistol and shot himself.
Mr Black described the harrowing moment he came face-to-face with the gunman after the struggle.
"So literally I'm looking down and he's looking up and we were staring right at each other. And at that point in time, I wanted to come down and put my knee or something to put it on his body to try to hold them down," he said.
Robert Dorgan killed two people, then himself, in the deadly attack at the Dennis M Lynch Arena | REUTERSMr Wallace-Hubbard also said her father never received the mental health support he needed.
'He never really saw the error in his ways. Yeah. I think without real substantial mental health help, I don't think he ever would have come around to see that, but you have to admit that you have a problem before you can get help. He was just not willing to do that,' she added.
Days before the attack, Dorgan posted ominous content on social media, including footage of someone loading ammunition into a handgun.
His daughter has launched a GoFundMe page for her surviving siblings Ava and Colin Dorgan, whose grandparents are now fighting for their lives in hospital.
That fundraiser has received more than $240,000 (£177,000) in public support.
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