Oct. 24, 2013— -- As Karl Karlsen awaits his trial for the death of his son, his daughter speaks out for the first time, telling ABC News' "20/20" that she has no doubts that her father is responsible for her deaths of her brother and mother.
"We knew what he had done to our mother," Erin, exclusively told "20/20." "And I knew what he did to my brother."
Karlsen, 52, is in a jail cell in Romulus, N.Y., facing charges of second-degree murder and insurance fraud in the death of his son and Erin's brother, Levi Karlsen.
In 2008, Levi Karlsen, 23, was crushed to death when the truck he was working on slipped off its jack and landed on top of him. His death was initially ruled an accident, but Karlsen collected a $700,000 life insurance payout after the incident, raising suspicions.
After a family member gave police a tip about the large insurance policy, authorities opened an investigation into Levi's death in 2012. Karlsen maintained that his son's death was an accident, and he pleaded not guilty.
Later that year, authorities in California also opened an investigation into the 1991 California house fire that killed Karlsen's wife and Erin's mother Christina Karlsen, for which investigators said he collected a $200,000 life insurance payout. Karlsen has not been charged with anything related to his wife's death.
Erin was just six years old when her younger brother Levi, and their sister Katie, escaped from the house fire that killed their mother.
"She was screaming, 'Karl, get the kids!'" Erin said.
Karlsen helped Erin and her siblings make it out of the house safely, where she said they stood and watched the house burn.
"At the time, I was six years old. I didn't understand that my mother was behind that wall dying," Erin said.
A week after the fire, Karlsen left California for upstate New York with his three children to be near his family.
As she got older, Erin said she was able to process what happened and came to believe that her father didn't do enough to help save her mother.
"You know, that's not how people are supposed to act when someone they love is trapped and literally burning in front of them," Erin said.
It wasn't until Erin and her brother Levi were 11 or 12 when she said they secretly discussed the possibility that their father wasn't being truthful regarding their mother's death.
"Between the two of us...we knew, because he didn't try," Erin said. "He didn't make an effort to save her. He just stood there."
However, when she and Levi confronted their father, Erin said, "his biggest concern was that he wondered what the community would think of his own children accusing him of murdering their mother."
While Erin and her sister Katie eventually left the small town where they were raised, Levi, who was divorced with two daughters, remained with their father and his second wife, Cindy Karlsen.
"He was basically an indentured servant to my parents," Erin said. "They were controlling everything. He wanted more than anything to just have a close relationship with our father."
After she received the news that Levi had died, Erin said she tried to put her suspicions of Karlsen's involvement in Levi's death at bay, but was relieved when she learned about the investigation into her father.
"It was never a question for me," Erin said. "It was a matter of fact."
When Karlsen was jailed, Erin said she went to visit her father and told him that she knew he was involved in her mother's and Levi's deaths.
"He won't ever own up to Levi," Erin said. "But he did tell me… 'It's been over 20 years, and they still haven't got me yet. What makes you think they're going to get me now?"
While she said she isn't angry with her father, Erin said she regrets not going to police sooner with her suspicions of her mother's death.
"What if I had said something earlier?" Erin said. "Maybe he'd still be here for his girls."
When Karlsen faces trial in two weeks, a judge ruled that testimony about the California fire and Christina Karlsen's death is off limits.
"I want him to look me in my eye and tell me exactly what he did," Erin said.
"Then I want him to go away for the rest of forever."