The couple had an argument that turned violent, and detectives found a knife “with biological evidence” at the scene, authorities said.
Police who went to the family apartment found a trail of bloody footprints and the body of Chaney, a 29-year-old US Air Force veteran. He had been stabbed in the heart.
“Their door was wide open, there was blood on the floor leading into their apartment, and then a trail of it in the hallway leading up to the elevator and I saw some blood on the walls,” one of Johnson’s neighbours told LA’s KABC-TV.
Johnson tried to drag her partner’s bloody body out of the apartment, but gave up and dragged the body back into the apartment kitchen, the Los Angeles Times reported.
After killing Chaney, Johnson then fled in a dark-coloured Porsche Cayenne SUV.
Shortly after, police and fire services were called to an emergency on the 405 in Culver City, about 16 kilometres west of LA.
Officials found Johnson’s infant daughter with major injuries and her older daughter with moderate injuries.
The infant was pronounced dead at the scene, while the older daughter was taken to hospital.
Johnson had slowed the car, opened the passenger door and then told her nine-year-old daughter, who was holding her infant sister in her arms, to get out of the car, police said.
“When the daughter didn’t do that she then forcibly pushed her out of the vehicle, in the middle of the freeway, while moving,” LA Police Department Lieutenant Guy Nolan.
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The infant was struck by a passing vehicle, authorities said.
After abandoning her children on the freeway, Johnson sped off at more than 160 km/h.
Half an hour later, she crashed into a tree in Redondo Beach, on the Pacific Coast Highway. Investigators believe the crash was a suicide.
Johnson’s body had been so disfigured in the crash that identification was difficult, the Los Angeles Times reported.
The surviving child has been placed in the custody of LA’s Department of Children and Family Services.
Police are still investigating a motive for the violent incidents.
“The only witness we have for this crime now is the nine-year-old girl,” Lt Nolan said. “There’s just very little information we have, other than: there was a verbal altercation that turned violent and it ended in tragedy.”
Johnson described herself in her Twitter profile as a “reiki master teacher”.
On her website, she offered “home purifying cleanses” and a daily “grounding” subscription.
Last Friday she posted on Twitter about the upcoming solar eclipse: “WAKE UP WAKE UP THE APOCALYPSE IS HERE. EVERYONE WHO HAS EARS LISTEN. YOUR TIME TO CHOOSE WHAT YOU BELIEVE IS NOW. IF YOU BELIEVE A NEW WORLD IS POSSIBLE FOR THE PEOPLE RT NOW.”
The Telegraph, London
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