In the case of Dorothea Puente, who murdered at least 7 people that were tenants at her house so she could continue collecting their social security benefits, why was the discovery of a dead body buried in her backyard not enough to arrest or detain her?
Alerted by the social worker, a detective went to her house to search for a missing person. After getting permission, the detective started digging in the backyard and found human remains. He calls in other police and they begin digging as well.
In this NYPost Article, it says Dorothea Puente was allowed to go meet her nephew for coffee down the street because they had no evidence to hold her. They had already found 1 dead body in her backyard.
Due to there being no evidence to link her to the body, she was allowed to leave – but managed to flee all the way to Los Angeles, where she was found five days later when a man in a bar recognized her from TV.
She was on parole at the time the detectives found the dead body.
Why was a dead body insufficient evidence to arrest or hold her and what evidence would have allowed them to arrest her after finding the body?
EDIT
The question is why is a dead body not sufficient evidence and what would have to change to make it sufficient? For example, would a bloody shovel be enough (no bloody shovel was found)? Would finding a missing person's ID be sufficient?