The Michigan man who gunned down his wife, nearly killed their daughter and was fatally shot by police had fallen down a “rabbit hole” of conspiracy theories leading up to the shooting, his other daughter said.

Lanis, a suburban Detroit auto industry employee, was arguing with his wife, Tina Lanis, 56, and daughter Rachel Lanis, 25, early Sunday when the two women were about to drive away from their home — but not before he opened fire with a shotgun, Rebecca Lanis said.

Rachel Lanis called 911 at about 4:11 a.m. Sunday and “stated that she had just been shot by her father” on Glenwood Drive in Walled Lake, the Oakland County Sheriff’s Office said in a statement.

When deputies and Walled Lake police arrived, Igor Lanis came out the front door with a Remington 870 pump action shotgun and shot at officers before they returned fire and killed him, the sheriff’s office said.

Tina Lanis was found dead, “shot multiple times in the back, and it appears that she was also attempting to flee out of the front door,” the sheriff’s office said.

The family dog, Sammy, also was found dead, shot multiple times.

Rebecca Lanis primarily blamed her father’s worsening mental state on QAnon, the false but widespread conspiracy theory about — among many other things — Trump’s leading a top-secret war on a cabal of pedophiles and criminals.

“In 2020, after the election, he started going insane. He went off the deep end," Rebecca Lanis said. "He started going down the rabbit hole of conspiracy theories and QAnon. First it started with the ‘stolen election,’ and then he started talking about worse things, 5G, the vaccine, just everything."

She said he began to believe that the "deep state stole the election and that there’s a worldwide cabal out to get conservatives.”