(CNN) -- Alabama police said Saturday that they believe they found the remains of the second of two siblings who allegedly suffered abuse at the hands of their father and his girlfriend.
Searchers near Citronelle, about 50 miles north of Mobile, found skeletal remains believed to belong to Natalie DeBlase, 4, whose father is accused of killing the girl and her brother Jonathan Chase DeBlase, 3, said Mobile Police Maj. Kara Rose.
Authorities on Wednesday found what they suspect are the brother's remains near Vancleave, Mississippi.
The father gave authorities general information on where the bodies might be found in the past week, Rose said.
The discovery of the remains believed to be Natalie DeBlase's was made in a densely wooded area around 9 a.m. Saturday.
John Joseph DeBlase, 27, is charged with two counts of murder and two counts of abuse of a corpse -- the latter because, Mobile Police spokesman Christopher Levy said, of his "disposing of the bodies in the woods."
DeBlase's girlfriend, Heather Keaton, was arrested last week, charged with two counts of willful abuse and neglect of a child.
Keaton waived extradition in Louisville, Kentucky, and is expected to arrive in Mobile on Sunday, Rose said.
"If it's appropriate to upgrade charges against Heather Keaton, they will be upgraded," Rose said.
Investigators continue to look at evidence and conduct interviews.
"It's a tough case," Rose said. "It has touched most of us."
The cause of death for both sets of remains has not yet been determined, police said.
Natalie, 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.
Police, who did not know the children were missing until November 19, contend that the elder DeBlase allowed Keaton to abuse the children by restraining them with tape, putting socks in their mouths and confining them.
Police believe both children died in Mobile, Levy said.
DeBlase and Keaton blame each other for the siblings' deaths, authorities said.
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.
According to the domestic violence petition, signed "Heather L. Leavell-Keaton," she 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.
The complaints were related to aggravated abuse allegations against DeBlase that were dropped and are now part of the murder charges.
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.