The baby died years before DNA became a crime-solving tool. Residents arranged for a funeral and burial and named the boy Andrew, which was inscribed on his gravestone. In 2009, a detective, hoping to use new DNA analysis methods to find a new lead, arranged for the body to be disinterred, according to court documents. But the baby's DNA profile wasn't closely related to any profiles in the state's crime database.Last year, police turned to investigative genetic genealogy, which seeks DNA links outside of crime databases. Investigators built a family tree that pointed them to Bentaas, according to court documents.
They used her trash to narrow it down further
New testing showed as you said that her family were likely relatives to the dead baby
How they already had DNA on one of them who knows could be many reasons from crime to hospitals or any other DNA gathering source
Suspecting the mom as the killer is pretty reasonable once you find out who she was ..either her or her family unless she was held hostage by baby killers at the time
The circumstances is definitely more to the story