READING, Pa. -- A woman who secretly conceived several children through an extramarital affair killed at least four of her newborns, then kept their remains in coolers or encased in concrete in her closet until family members found them this year, authorities said Monday.

Michele Kalina, 44, of Reading, hid at least six pregnancies from her husband and longtime boyfriend, according to officials in Berks County, where a homicide charge was filed against the home-health aide.

DNA tests show the bones found in a locked closet came from five babies, at least four of whom were born alive, authorities said. The boyfriend fathered three and possibly four of the victims. Tests on the fifth baby were inconclusive.

Dogs trained to search for human remains have scoured Kalina's current and former homes in the Reading area.

"I'm very confident we have all the babies," District Attorney John T. Adams said at an afternoon news conference.

Kalina has been in custody since August on abuse-of-corpse charges and is being held without bail after she was arraigned Monday on one count of criminal homicide, aggravated assault and related charges. Additional counts may be filed before trial, Adams said.

A preliminary hearing is scheduled for Thursday. Public defender Holly Feeney declined to comment Monday.

Kalina also bore a daughter from the same affair in 2003 but gave the baby up for adoption, authorities said. She and her husband, Jeffrey, have a 19-year-old daughter and had a 13-year-old son with cerebral palsy who died in 2000. That death is not suspicious, Adams said.

The husband and daughter found the infant remains this summer in a closet in several coolers, one of which was filled with cured cement, police said. At least four of the babies were born at or near term, then killed in a manner consistent with asphyxia, poisoning or neglect, authorities determined.

With only scant information from Kalina herself, investigators have no idea where the babies were born or how they died, making the case a tough circumstantial one to prove.

However, Adams said he believes Kalina's brief statements to police after the remains were found, and her reaction to their involvement, show evidence of a guilty conscience. She told authorities she had been pregnant only twice, with her son and daughter, and had never had a stillbirth, Adams said. And she fled her family's apartment after learning police had been called about the bones in late July.

The officers who first responded to a 5 a.m. call from her daughter did not think the bones were human and said she and her father could throw them out, which they did. Later that day, the pair called again to say they had found additional remains. Investigators then suspected they were indeed human.

One bone -- from the remains that were thrown out -- was later found at a landfill but did not provide enough evidence for officials to determine whether the baby was born alive, authorities said.

Jeffrey Kalina had suspected at least once that his wife was pregnant, police said. The boyfriend, who was not identified, said he did not, although he said he noticed her abdomen growing after they began dating in 1996.

Kalina told him she had cysts on her fallopian tubes that she had drained at a hospital, he said. The "cysts" returned several times over the years, he said.

"She always had a job where she wore scrubs," Adams said.

Kalina has what Adams called an "exemplary" work history, with 14 years on the job and no maternity or extended medical leaves. Her employer, a home-health agency, declined to comment Monday.

Police did not find any records to show she got prenatal care or gave birth in local hospitals, except for the hospital birth of the daughter who was adopted. The boyfriend told police he did not know about that child, either.

"He had no idea," Adams said.

Kalina told police she is an alcoholic prone to blackouts.

Until her arrest, she lived in a high-rise apartment with her husband, who is disabled, and their daughter. Jeffrey Kalina told authorities that the containers had been moved to the apartment with other belongings from their prior home in Reading in 2008.

In interviews in early August, Kalina told police she had forbidden her husband and daughter from going in the closet, according to the police affidavit.

"Michele Kalina further stated that she had been meaning to clean that closet," the affidavit states.