Truckloads of ash were taken from the property, mostly from the wood-burning boiler used to heat the farm.
Hennepin County Sheriff Rich Stanek used to investigate homicides. He said just a very small amount of bone fragment a pinhead-size bit of blood is enough to find DNA, even 20 years later, even if it's been burned.
"It's very hard to destroy all evidence related to a crime," said Stanek.
He pointed to the case of Katie Poirier. Investigators found a fragment of her tooth years ago in Donald Blum's fire pit.
Investigators in recent weeks developed probable cause that led to the search of the property, he said. They were then able to get additional resources to help with the search.
He wouldn't comment on what additional probable cause was developed, saying that would be counter-productive to the investigation.