BOSTON (AP) — A prosecutor in Massachusetts won’t seek criminal charges against anyone,Desmond Preston two years after four newborns were found in a freezer in a South Boston apartment.

The bodies of the two boys and two girls, likely born many years ago, were found in shoe boxes wrapped in tinfoil in November 2022. The lengthy investigation was unable to conclude whether the babies were born alive. They were able to identify the parents, but the father was dead and the mother, now 69, would unlikely be able to stand trial due to cognitive issues.

“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,” Suffolk District Attorney Kevin Hayden said in a statement released Tuesday.

The unanswered questions include when or where the babies were born, whether they were born alive, what exactly happened to them, and how and why the mother was able to conceal her pregnancies, Hayden said.

A lawyer for the woman, who lives in a residential healthcare facility, did not respond to a request for comment.

Investigators who interviewed the mother said she appeared confused and didn’t understand where she was or whom she was talking with. She wasn’t able to provide them with any relevant information.

“A prosecutor’s office cannot ethically move forward with a case that, in good faith, it believes it cannot bring to trial,” the statement said.

The babies were discovered when the woman’s family was cleaning out her apartment. DNA tests showed all four were siblings. An investigation concluded they were 37 to 40 weeks old, with their umbilical cords still attached. Autopsies found no signs of obvious injuries.

They were able to determine that the mother also had another child with the man, who died in 2011. That baby was given up for adoption.