(CNN) -- Police have ratcheted up charges against the girlfriend of an Alabama father, days after searchers found fragmented remains they say are of the second of the man's young children, tossed along the side of a remote highway.
Mobile, Alabama, police spokesman Christopher Levy said Monday that Heather Keaton would be charged with two counts of aggravated child abuse and two counts of abuse of a corpse -- one count each for the deaths of Jonathan DeBlase, 3, and his sister Natalie, 4.
The children's father, John Joseph DeBlase, 27, was arrested December 3 and is now charged with two counts of murder and two counts of abuse of a corpse.
John DeBlase's lawyer, Jim Sears, said Monday that his client maintains "his innocence in regards to the death of the children." Sears added that DeBlase might consider pleading not guilty by reason of disease or mental defect (equivalent to an insanity plea in other jurisdictions).
The investigation kicked off November 18, when Keaton told Louisville, Kentucky, police that she needed protection from DeBlase, who she claimed was holding her against her will. She was arrested in early December and charged, at the time, with two counts of willful abuse and neglect of a child.
Around 1 a.m. Monday, Keaton arrived from Kentucky to face the four additional charges, according Levy. By early in the afternoon, she had not been questioned by Mobile police.
Her arrest followed the discovery Saturday morning of remains that authorities believe are those of young Natalie DeBlase.
Searchers had planned to canvas woods abutting a six-mile stretch of highway just northwest of Citronelle, Alabama, about 50 miles north of Mobile, based on information provided by John DeBlase. But they found the remains -- less than half of a young body, including a skull and miscellaneous bones -- around 9 a.m., within 30 minutes of starting the search.
"We didn't cover hardly any of it, because we found her so quickly," said Levy. "She was where he said she would be."
Levy said the girl was not buried, but had been laid "in the woods, not far from the roadway," just as DeBlase had told authorities.
The Alabama Department of Forensic Sciences is examining the remains to confirm that they belonged to Natalie.
The girl was last seen in March, when authorities believe she was killed. Jonathan DeBlase had not been seen since June, police said. Investigators believe he was slain around that time.
Remains that police believe are those of the young boy were found last Wednesday near Vancleave, Mississippi. The cause of death for both sets of remains has not yet been determined, police said.
DeBlase and Keaton blame each other for the siblings' deaths, authorities said.
Police, who did not know the children were missing until November 19, contend that DeBlase allowed Keaton to abuse the children by restraining them with tape, putting socks in their mouths and confining them.
A day earlier, Keaton signed a domestic violence petition in Louisville that said, "I feel he may have murdered his children, because he said they were non-responsive. He would not let me check on them."
She said DeBlase had told her "choices were made ... and he had to do what he had to do."
According to a police complaint, DeBlase between March 1 and November 19 allowed Keaton to tape Natalie's hands and feet, put a sock in her mouth and place her in a suitcase that was put in a closet for 14 hours.
He also allowed Keaton to tape Jonathan's hands to the side of his legs, tape a broom handle to his back, place a sock in his mouth and then make the child stand in a corner all night when the couple went to bed, according to the complaint.
DeBlase and Keaton have one infant daughter together, according to Keaton's account in the Kentucky police report. Police said one reason Keaton claimed she needed protection from DeBlase was that she feared for the safety of the infant, who was with her in Kentucky.
HLN's Natisha Lance contributed to this report.