17 Nov 2021
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It's the equipment police are hoping can help provide a breakthrough after seven years of dead ends.
And, officers have returned to where it all began - the front yard of William Tyrrell's foster-grandmother's house - to use it.
William disappeared aged three in September 2014, and despite a massive police investigation, no one has ever been charged and no body has been found.
On Tuesday, Australian Federal Police (AFP) specialists joined the operation.
Law enforcement and Rural Fire Service (RFS) volunteers are expected to search three new locations in and around the town of Kendall, on the NSW Mid-North Coast, over the next three weeks.
"There will be a number of strategies used by the police and other agencies to clear ground and go subterranean in the number of locations," Detective Chief Superintendent Darren Bennett said this week.
Here are some of the tools they'll be using.
A police cadaver dog is seen near the former home of William Tyrrell's foster-grandmother.(AAP: Mick Tsikas)
Cadaver dogs have been brought in to scour parts of the front yard, particularly the garden beds and an area below the home's balcony.
They have also been taken into bush about 1 kilometre from the house.
They are trained to find the scent of a decomposing body and then alert their handler to the location of the remains.
They can sniff out remains that are decades old, even if they are buried.
Even with technological advancements, dogs are still considered among the best tools for odour detection in policing.
Cadaver dogs can detect the smell of human remains, blood, clothing from a decomposing victim or human fluids associated with remains.
Police dogs were brought to the scene shortly after William disappeared in 2014 and they detected his scent but only within the property's boundaries.
Police use luminol
Forensic police use luminol and a blue light to look for blood.(AAP: Mick Tsikas)
Forensic investigators have been using a substance called luminol around the front garden of the house on Benaroon Drive.
William's foster-grandmother had lived in the property. She died in March.
Luminol is a substance used to find traces of blood and can give detectives clues about exit routes from crime scenes or whether a body has been dragged somewhere.
It reacts with the iron in haemoglobin, a protein found in red blood cells.
Traces of blood emit a blue glow once sprayed with luminol.
Luminol is particularly useful if there is only small traces of blood that are not visible to the human eye or if an attempt to clean up blood has been made.
Ground penetrating radars
Police use ground penetrating radar
Police use a ground penetrating radar during the search for William Tyrrell's remains.(ABC News: Kamin Gock)
Ground penetrating radars (GPRs) use radio waves to capture images below the surface of the earth.
They are a key tool for investigators trying to locate buried objects and can even identify whether a hole was once dug at a location.
They can detect objects under wooden floors and brick or concrete walls and have been used in many cold cases if someone is believed to be buried.
GPRs save lengthy and costly excavations and were used by British police in their investigations into the notorious serial killer Fred West.
By using the radar technology, officers were able to uncover the bodies of nine women in the backyard of West's house in Gloucester which became known as the "house of horrors".
Sifters, metal detectors and drones
Police use sifter
Police use a mechanical sift at the site where William was last seen.(AAP: Mick Tsikas)
Police are also using sifters to go through the soil on the Kendall property as they look for clues.
It is a common tool used by forensic teams but can be very time intensive as it involves sifting through mass amounts of dirt and debris.
On Tuesday police were seen sifting soil from the garden bed at the Kendall home.
Metal detectors are also being used on the property and the AFP is using drones to survey the area.
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