A 14-year-old Indiana boy was being held at a juvenile detention center after confessing to the suffocation deaths of two younger siblings, authorities said.

The first child, a 23-month-old girl named Desiree, died in May, five days after being hospitalized for “not breathing right,” mother Christina McCartney told FOX 19 of Cincinnati.

A few months later, McCartney's 11-month-old stepson, Nathaniel Ritz, died after being suffocated, the report said.

Soon after the boy’s death, the children’s 14-year-old brother confessed to killing them, authorities in Ripley County, Ind., said.

But McCartney spoke out in defense of the teen.

"He's not the monster that people are trying to portray him as,” she told the station. “It's a mother's worst nightmare to have such a precious family and then to wake up to the worst possible outcomes.”

“It's a mother's worst nightmare to have such a precious family and then to wake up to the worst possible outcomes.” — Christina McCartney, mother of teen suspect and slain children

The teen told investigators that he killed the children so that they wouldn't "have to live in the hell that he did," prosecutors allege, though the meaning of the teen's words wasn't clear.

Ripley County Prosecutor Richard Hertel said Wednesday that the teen was arrested last week on juvenile charges of murder in the deaths, which occurred at the family's home in Osgood, a rural community about 60 miles southeast of Indianapolis.

In a probable cause affidavit filed in court, authorities say the teen, who was 13 at the time of the deaths, told investigators that he used a towel to suffocate his half-sister and a blanket to kill his stepbrother.

Hertel said the teen was advised of the charges he faces at a Monday court hearing, after which the judge said he'd rule on whether the teen is competent to stand trial before deciding whether to grant prosecutors' request that he be tried as an adult.

The boy was charged following a State Police investigation that Hertel said was ongoing.

According to the affidavit, the teen told investigators who questioned him about his siblings' deaths that "he had a conversation with God about them, but he could not talk about it because he had promised God he wouldn't tell anyone."

Under further questioning, the teen began "talking about saving Desiree and Nathaniel from hell and the chains of fire," it states. He then added that "he didn't want them to have to live in the hell that he did," before going on to describe how he suffocated the children.

When asked what that "hell" was, the boy replied "chores," before asking investigators if they'd seen the list of daily chores he had to complete, the affidavit states.

According to the affidavit, the teen's grandmother told investigators that when she asked him why he killed his siblings, he replied that "he didn't want them to be treated the way he had been." She said he also described how he'd firmly held the towel and blanket over their heads to suffocate them.

An uncle told investigators that the day before Nathaniel Ritz's death, the teen told him that Ritz's father had bloodied the teen's nose.

Hertel said the teen's motivations remained unclear, but that doctors who will examine him may be able to shed light on them.

"In my time here, which has been 19 years, I'm not sure that I've seen anything quite as disturbing and as final as something like this," he said during a news conference in Versailles, the county seat.

The prosecutor said that shortly before the teen's half-sister's death, the boy squeezed a kitten so hard its insides came out, telling relatives it had scratched him.

Hertel said the suspect's father is currently in prison and that he believes the boy's mother is cooperating with the investigation.

Neighbor Becky Horn told WLWT-TV that the children's deaths stunned the small community.

"Our whole street, we were in tears for weeks over this," Horn said.

The Associated Press contributed to this story.