MOBILE, Ala. (AP) - An Alabama man charged in the slayings of his two young children who police say were dumped in the woods will plead not guilty, an attorney said Friday, citing "mental disease or defect."

John DeBlase, 27, is charged with two counts of felony murder and two counts of corpse abuse in the children's deaths. Skeletal remains found Wednesday in the woods of rural Mississippi are believed to belong to his 3-year-old son Chase. Authorities have not found the remains of his daughter, Natalie DeBlase, who would have turned 5 in late November.

DeBlase appeared in court Friday in Mobile and was ordered held on $500,000 bond.

Attorney John Thompson told the judge that DeBlase, who stood silent throughout the hearing, planned to plead not guilty by reason of mental disease or defect. DeBlase's court-appointed attorney, who was out of town Friday, said in a telephone interview after the hearing that the plea was "pretty standard," and that DeBlase's mental state will be reviewed before trial.

"We're going to be investigating a lot of different aspects of him personally, as well as the evidence," lawyer Jim Sears said, adding that comments made by friends that called into question DeBlase's mental health are "certainly not without reason."

Lisa Moseley Schreiner, who said she was the children's godmother, told The Associated Press that DeBlase "was a little slow." She said she has known him for about eight years.

Sears has said DeBlase maintains that he is innocent and that his common-law wife, Heather Leavell-Keaton, killed the children.

Leavell-Keaton had been held in Kentucky but is being transported back to Mobile to face charges. She is due to arrive Sunday.

Mobile County Assistant District Attorney Jo Beth Murphree said Friday that authorities would soon be upgrading Leavell-Keaton's charges from child abuse to more serious aggravated child abuse counts. She also was to be charged with two counts of corpse abuse.

Prosecutors have not yet filed murder charges against Leavell-Keaton, but police have said she and DeBlase share responsibility for the killings. Each has blamed the other for the children's deaths.

DeBlase told police he dumped his daughter Natalie in the woods north of Mobile in March. He said he discarded the boy's body, dressed only in a diaper and stuffed into a plastic garbage bag, in Mississippi in June on or around Father's Day. Police say the children were killed separately, then immediately disposed of.

Arrest warrants in the case accuse Leavell-Keaton of abusing the boy and girl.

The documents were prepared before the murder charges were filed and accuse Leavell-Keaton of mistreating the children. They say DeBlase allowed her to bind the girl's hands and feet with duct tape, put a sock in her mouth and stuff her in a suitcase in a closet for about 14 hours.

The warrants also accuse Leavell-Keaton of duct-taping the boy's hands to the side of his legs, strapping a broom handle to his back and shoving a sock in his mouth, then forcing him to stand in a corner all night while the adults went to bed.

The documents say the abuse happened sometime after March 1.

DeBlase and Leavell-Keaton were arrested last week on the abuse charges, and authorities began their search for the children's remains in Alabama and Mississippi over the weekend. Neither child had been seen for months.

An investigation into their disappearance didn't start until late last month after Leavell-Keaton sought a protective order against DeBlase in Kentucky, said Mobile Police Officer Chris Levy.

She said in the Nov. 18 filing that DeBlase may have killed his children, and that she feared for her life because he was abusive. The couple had a child together this summer. That child is in state custody in Kentucky. "I am afraid that he is going to do something to harm our daughter because of what he has done to the other children," she wrote.

(Copyright 2010 by The Associated Press. All Rights Reserved.)