Massachusetts prosecutors announced on Tuesday that the mother of four infants found dead in a freezer in 2022 will not be criminally charged.

The full-term babies, two boys and two girls, were in shoe boxes wrapped in tin foil in the freezer. Boston police were called to Alexis Aldamir’s apartment after a man reported finding the bodies while cleaning out the home with his wife, according to Boston.com.

The four babies reportedly had their umbilical cords attached, and the two girls also had their placenta attached. DNA testing confirmed the four babies were siblings, but the medical examiner could not ascertain a cause of death or how long they had been frozen.

Suffolk District Attorney Kevin Hayden said it also remains unclear whether the babies were born alive.

“We will never know exactly what happened to them. We will never know how Alexis Aldamir concealed her pregnancies, or why she chose to do so,” he said.

Aldamir, 69, was living in a residential healthcare facility when police obtained a DNA sample that identified her as the mother of the four deceased babies. Testing also confirmed that the father was a man who died in 2011.

Boston.com reported that the man and Aldamir had a baby girl in 1982 who they gave up for adoption.

Investigators said they questioned Aldamir about the dead babies in her apartment, but she “appeared confused and demonstrated a lack of understanding about where she was and who she was speaking to,” according to WFXT. Hayden also said it is very likely Aldamir would not be fit to stand trial given her mental state.

“This investigation, which is one of the most complex, unusual, and perplexing that this office has ever encountered, is now complete. While we have some answers, there are many elements of this case that will likely never be answered,” he concluded.