SACRAMENTO (CBS 5) – Police arrested a Northern California mother Tuesday on a murder charge, saying they believed she had burned her six-week-old baby to death in a microwave oven.

Ka Yang, 29, of Sacramento, had apparently claimed the young child’s March 17 death at home was caused by a seizure.

But the Sacramento Coroner determined Mirabelle Thao-Lo died from burns, however it could not be determined how she got them. After a three-month investigation that included consulting with several medical professionals and forensic specialists, police said they concluded that Mirabelle died as a result of being burned in a microwave oven.

Police described the child as suffering “extensive thermal injuries.” Officer Laura Peck said the arrest took so long because investigators had to pinpoint what they believe is the cause of death by looking for other cases involving similar injuries.

They found three in the U.S., all after children were burned in a microwave: in Dayton, Ohio; Galveston, Texas; and New Kent County, Virginia.

“This is rare. The injuries were obviously very unique,” Peck said. “There have been only three other documented cases in the entire country where the injuries were consistent with this case. … Those children were also burned and placed in the microwave.”

Yang was booked into the Sacramento County Main Jail on Tuesday and charged with one count of homicide.

Peck said police do not know a motive. She did not believe Yang had an attorney, and none was listed in jail records.

“We wouldn’t assess her mental condition. That will be up to the court system,” Peck said. “The bottom line is no one knows what happened in that house but her and the little baby.”

Yang has three other children, all under age 7, who were removed from the home the day their sister was found dead. They are now living with relatives.

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