A deadly explosion at a Southern California office building is being investigated as a crime, and the woman killed is believed to be the owner of the business where the blast took place, according to authorities.
The cause of the blast remained a mystery for much of the day, with officials initially believing a auto had smashed into the building.
Sheriff's officials said the size of blast made it suspicious.
The Orange County Sheriff's Office, the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosions continued to investigate.
A neighbor there who would only give her first name as Tiffany said Krajnyak lived there with her estranged husband and mother, whom she cared for. She said she saw two burned women staggering out of the building, covered in ash and soot.
The officials said the explosion did not appear to be part of a broader plot and there was no immediate connection to any extremist groups.
A still from surveillance cameras provided by Kennedy Chiropractic shows investigators as they probe an explosion at an Aliso Viejo building on May 15, 2018.
Orange County Sheriff's Department spokeswoman Carrie Braun says investigators worked through the night and were still at the scene Wednesday morning.
But police have not confirmed this and they say no device was found.
Orange County Sheriff's Cmdr.
The woman who was killed inside the building was "in close proximity" to the explosion, Sawyer said.
"We do not know the motive behind the case at this time", Orange County Undersheriff Don Barnes told reporters at a press briefing at sheriff's department headquarters in Santa Ana.
Prior to Barnes identifying the victim, her son told KTLA in a telephone interview that the family hadn't heard from Krajnyak since the explosion.
Earlier, a law enforcement source told CNN that the explosion may have been detonated on goal, but the source also cautioned that the investigation was in its preliminary stages.
Two other people were injured.
A USA official told The Associated Press that the explosion is believed to have been intentional and may have come from a package.
Pieces of the explosive device recovered were sent to the FBI's laboratory in Quantico, Virginia, to be analyzed, Delacourt said.
The dead and injured have not been named.
The blast blew siding off the walls, exposing insulation and framing and shattering windows at the two-story building that houses medical offices.
A federal official told The Associated Press late Tuesday that the explosion is believed to have been intentional and may have come from a package.
Shin said it felt like "a big natural disaster", and as he and others rushed downstairs to get out of the nearby building, he saw two holes in the wall of the medical facility.
Fennessy says the blast involved a building under renovation. A third person suffered smoke inhalation.