By Mike Dougherty

PHILADELPHIA (CBS) — A large contingent of law enforcement officers spent several days searching for human remains on a farm in Bucks County last week.

A former FBI agent shared some of the tricks of the trade that eventually led to the gruesome discovery of four bodies.

Searching begins with highly trained canines.

“These cadaver dogs have unbelievably sensitive senses of smell,” said former FBI spokesman JJ Klaver.

Klaver says, like drug or bomb sniffing dogs, the cadaver dogs have laser focus on the smell of human remains and were able to pick up the scent nearly 13 feet below ground.

“Once the cadaver dogs kind of start hitting on a certain area and they are going to start digging, the next thing they are going to deploy is some technological means to try and determine how deep they need to go,” Klaver explained.

Ground-penetrating radar and sophisticated metal detectors show the depth of solid objects below the surface, then it’s time to dig by hand.

“They presume bodies are there, a body or bodies, so they can’t just bring in a backhoe and start digging and sifting,” said Klaver.

That back-breaking digging in the middle of a heatwave was essential to preserve the evidence found.

“For the forensic pathologist to determine the cause and manner of death,” Klaver said.

Klaver says even though there was a confession, evidence must be collected carefully in case there is a trial.

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