Nikolay Soltys was charged Tuesday with seven counts of murder in the deaths of six family members and his unborn child.
The 27-year-old Ukrainian immigrant told police he killed six of his family members, including his pregnant wife, because they were "poisoning" him.
Sacramento County District Attorney Jan Scully said she could file charges in the murder of a fetus, as long as the fetus was at least seven to eight weeks old.
"Baby Soltys is the seventh victim. It's appropriate that he be charged for all victims," Scully said before the Tuesday afternoon arraignment.
All seven counts against Soltys include special circumstances of using a deadly weapon, making him eligible for possible sentences of life without parole or the death penalty. Scully said she hadn't made the decision to seek the death penalty.
Soltys was found hiding under a desk in his mother's back yard in Citrus Heights Thursday after leading investigators on a 10-day manhunt and landing on the FBI's Most Wanted List.
After his capture, authorities said, Soltys told detectives he killed his pregnant wife, 3-year-old son, aunt, uncle, and two 9-year-old cousins and showed deputies the abandoned home where he said he had been hiding.
On Thursday, when police found Soltys, who was filthy and had several days' growth of beard, they also found a backpack and sleeping bag nearby. Inside the pack was a 10-inch knife police believe Soltys used to kill his relatives on Aug. 20.
Authorities, however, said they don't believe Soltys returned to his mother's home to harm others.
"The impression was he was not coming back to kill them," said Sacramento sheriff's Sgt. James Lewis. "It was more a reaching out to the family."
In a note Soltys left in his abandoned vehicle, he explained the alleged rampage, saying he killed the cousins to punish their parents for speaking out against him, investigators said. He offered no explanation for the killing of his son - hours after he allegedly stabbed his wife to death.
© MMI, CBS Worldwide Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report