A Pennsylvania mother who told police she found her two children hanging dead in their basement after her son “made threats of doing this, but didn’t want to go alone” has been charged with their murders, authorities announced Monday.

Prosecutors allege Lisa Rachelle Snyder, 36, murdered her son, Conner, 8, and daughter, Brinley, 4, inside their Albany Township home on Sept. 23 before covering up the crime to make it look like a bullying-related suicide.

“Eight-year-olds, generally, that I am aware of, do not commit suicide. So of course we had questions,” Berks County District Attorney John Adams said in a Monday press conference, adding that “this is a horrific, tragic incident.”

Snyder was arrested and charged Monday with first-degree murder, tampering with evidence, endangering the welfare of children, animal cruelty, and sexual intercourse with a dog, Pennsylvania State Police said. She’s being held in Berks County Jail without bail.

“I don’t know there is any explanation for her behavior at all. I don’t think I can stand up here, nor anyone, and explain the horrific loss of two innocent children’s lives,” Adams said. “I think it goes without explanation.”

Authorities allege the day before the children were found, Snyder searched on the internet for information about “hanging yourself,” “how long to die” from carbon monoxide, and the Investigation Discovery true-crime television series Almost Got Away With It, according to a probable cause affidavit obtained by The Daily Beast.

On Sept. 23, Snyder told authorities she found her two kids unresponsive in the basement of their home after the pair had gone “downstairs to build a fort.” The mom claimed she was putting laundry away and smoking a cigarette outside when Conner took dining-room chairs and a dog leash to the basement, according to the affidavit.

Snyder said when she got downstairs, she tried to take her children down, but was unable to lift to them and called the police, the affidavit states. The mother of two never returned to the basement after calling authorities, prosecutors said.

“I would agree that we all may think that a mother of a children who are found hanging would make every effort possible to save them,” Adams said. “That was not done in this situation.”

According to a search warrant, two emergency responders who arrived at the scene first found the two children hanging three feet apart from a “single wired cable with plastic coating and ends containing swivel eye snap hooks” with two wooden chairs knocked over nearby.

In the transcript of a call between a Berks County emergency dispatcher and the first responders obtained by The Morning Call, a fire captain asks: “Any indication from the caller if the scene is safe or how these children ended up there?”

“She mentioned that the 8-year-old has been bullied and has made threats of doing this, but didn’t want to go alone… At this time, it should just be the mother and the two children on scene,” the dispatcher responded.

In two separate interviews, Snyder allegedly told police her son was suicidal after he had been bullied because of his weight—prompting him to lose “25 pounds since school started because he was starving himself.”

“He tells me he hates school, every day he tells me he doesn’t want to talk about school. I did not really see any problems till he told me about the kids on the bus,” Snyder told authorities, according to the court documents. “He just comes home and he is just angry.”

Later, the mother told investigators her son also suffered from a speech delay, which she alleged made him “a little slower to grasp things,” the affidavit states.

Snyder told officials that at one point he said, “I woulda killed myself already, but I am scared to go myself.” Conner was a third-grade student at Greenwich-Lenhartsville Elementary School, which denied the boy was bullied prior to his death.

“Conner was a beloved member of the Greenwich Elementary School family who enjoyed his peers and teachers,” Kutztown Area School District Superintendent Christian Temchatin previously said in a statement to The Daily Beast. “He is dearly missed and is fondly remembered for the smile he brought to all who knew him.”

The affidavit states another person who lived in the home—only referred to as “witness 3”— told authorities the two children never played in the basement and the 8-year-old never mentioned being bullied. Another witness told authorities that three weeks before the incident, Snyder told her she was depressed and “made a statement that she does not care about her kids anymore.”

Adams said Monday the 10-week investigation found that Conner “appeared to be a happy child” and that the only person to claim the 8-year-old was bullied or depressed was his mother.

A certified occupational therapist who worked with Conner also told authorities he received therapy due to his “below average visual motor skills” and suffered with “difficulty with dexterity.”

This “poor dexterity,” the therapist told police, would make it difficult for Conner to operate the clasp on the dog leash and wrap it around a basement beam, according to the affidavit.

“Conner would have had a difficult time finding the middle,” the witness said, describing the child as “clumsy.”

The siblings were revived in a helicopter on the way to Lehigh Valley Hospital, authorities said, but died in the intensive-care unit three days later. The Lehigh County coroner’s office told The Daily Beast on Monday the two children died from hanging and their death has been ruled a homicide after an “extensive investigation.”

Pennsylvania State Police immediately opened an investigation into the children’s deaths, seizing a number of items from the scene and executing at least five search warrants. According to the warrants, police took a wire cable, two wooden chairs, two iPads, a computer, and an Xbox game system from the family’s home.

Another warrant issued Oct. 2 requested the family’s dog, a black, 50-pound husky/pit bull mix that is still missing.

According to the affidavit, Snyder also sent at least three sexually explicit photos of herself engaging in various sex acts with a black and white dog to an unidentified person in the weeks leading up to the slayings. The photos were found in her email during the investigation.

“It is very emotional for all of us,” Adams said. “To have two children taken at such a young age, what appears to be two very innocent people. It’s not right, it hits us in the heart.”

The state Department of Human Services also previously confirmed that “ongoing case management services” were provided to the Snyder family through Berks County Children and Youth Services, but declined to provide details. Adams said on Monday the two children had been taken from Snyder in 2014 and were returned in February 2015.