Photos from the revived search for William Tyrrell have offered a grim insight into what detectives are trying to find.
Detectives who this week returned to the property where William Tyrrell was last seen seven years ago are likely sifting through soil in search of the little boy’s remains, a forensic expert has revealed.
Police on Tuesday resumed their search at William’s foster grandmother’s home on NSW’s Mid North Coast, where they were pictured filtering through sections of dirt using giant sieves.
Such a tactic was typically used by investigators when searching for human remains, forensic expert from the Victorian Institute of Forensic Medicine, Professor David Ranson said.
“It’s a common piece of equipment to be using particularly when you’re looking through a site where there might be fine remains like teeth or small bones of the hands, which can get scattered,” Prof Ranson told news.com.au.
Remains, especially if they were not deeply buried, oftentimes were found significant distances apart due to being uncovered and transported by animals, he said.
“So if you’re looking in an area where there might be some small remains or bone fragments, you would use a series of graduated sieves to go through the soil to try and identify larger pieces of tissue or bone.
“Because once things get contaminated with soil they can look like bits of stone, so you need to be able to sieve all the stuff out and look carefully at the things that are left over.”
The type and condition of the soil on the property would play a key role in the search, Prof Ranson said, given remains would be affected differently depending on the environment.
He said police would be taking into consideration things like how protected the area was, if there was nearby water flow, and whether the soil was clay, acidic or sandy.
“All of these soil characteristics play a part in how easy it is to find remains and what condition remains might be in,” he said.
The condition of remains would also be influenced by whether they were kept in something like a sealed heavy duty plastic bag or laid in a shallow grave, Prof Ranson said.
“Obviously when you start the investigation you have to consider that any one of these might be the situation you find yourself in, and you have to prepare your technical side to manage that particular scenario,” he said.
Methods used to find site
Police had access to a variety of modern techniques to help find a potential site of interest, including aerial photography and heat detection devices, as well as analysing vegetation regrowth and changes, ground contour changes, and changes to soil colours, Prof Ranson said.
They would also potentially follow tracks made by animals if they suspected a body to have been buried in a shallow grave.
“These are remains where often there’s animal predation, and animals will carry away small bits of body and move them to different areas,” he said.
“One of the things you often do is follow dog trails in the area. You might follow them to see if there are any other remains in a little den or something like that.”
Police Minister David Elliott confirmed on Tuesday experts from the Rural Fire Service had been brought in to inspect the soil in the area.
“We’ve got an excellent Rural Fire Service here in NSW. They are experts in managing the ground, in identifying any soil that may have been moved, in any ground that’s been disturbed, and that’s what they are looking out for,” he told Today.
Soil exploration offers vital clues
A soil probing device could also offer detectives vital clues in their search for William, Murdoch University forensic scientist Dr Paola Magni said.
The device is a long thin pole that, once inserted into the soil, returns detailed information about the soil below without the need for anyone to dig it up.
Dr Magni said the probe would be able to detect changes in the soil if it had been contaminated by human remains.
“Organic matter will release gas and liquid so the soil surrounding something organic will have a different texture and consistency,” Dr Magni told news.com.au.
If the probe alerted to organic matter, detectives would then use a sieve – like that used by NSW Police on Tuesday – to filter through the soil.
“It’s used to see if you can find anything related to a human like a nail, a tooth or a ring,” Dr Magni said.
A ground penetrating radar (GPR) was another device detectives would likely be using in the search for remains, as it uses radio waves to capture images below the surface of the ground, without having to dig.
The device would be capable of locating a “hot spot” beneath a section of grass or bushland, even if it had been untouched for years.
“You could have a hot spot of plants because organic matter is like fertiliser. So you could have a spot of a lot of grass that doesn’t make any sense,” Dr Magni said.
She explained that, depending on the environment and conditions, a distinct lack of plant life could also be indicative of something having been disturbed beneath the soil’s surface.
“In some cases you could even have a hill in a specific spot, so you have to look for inconsistencies in the environment and work from that,” she said.
Physical search for William revived
Police on Monday revealed they had revived a physical search for William, deploying hundreds of officers across three locations in the area he went missing.
William was playing with his five-year-old sister in the yard at his foster grandmother’s house on Benaroon Drive, Kendall, on September 12, 2014, when he disappeared.
He was three years old at the time and was last seen wearing a Spider-Man costume.
Police have been pictured removing plants and debris from the home’s garden, with officers reportedly using Luminol – a substance that reveals traces of blood.
A cadaver dog had also been put to work at the scene.
Strike Force Rosann detectives have investigated hundreds of leads and several suspects as part of their ongoing search, with a $1 million reward still on the table for help finding the missing child.
Detectives first revisited the Kendall area in September after new information had “come to light”.