The investigation into what happened when William Tyrrell went missing seven years ago is gaining momentum.
Police are working on a theory that he fell from a balcony, with his foster mother becoming the centre of their investigation.
Police have been using blue luminol lights on garden beds, over dirt and on walls at Tyrrell's foster mother's house.
They're searching for blood that is seven years old.
"They're looking at whether William may have fallen off the balcony. If that has happened there is likely to be significant blood loss and that would show up even years later," criminologist Dr Xanthe Mallett told Sunrise on Channel 7.
Forensics are hoping to find evidence that will bolster the investigators' current theory.
They currently believe that on the morning of September 12, 2014, Tyrrell fell to his death.
A photo of Tyrrell wearing a Spider-Man costume was taken at 9:37am on the day he went missing.
Between then and 10:57am - when his foster mum called the police saying "he's wearing a Spider-Man outfit" - it's believed his body was driven in a grey Mazda to a location 1km away.
Police will spend the next few weeks at the location, looking for the missing boy.
His foster mum is now under the spotlight after being charged alongside Tyrrell's foster dad with the unrelated alleged assault of a child who is not William.
Previously, police didn't consider them suspects.
"At the time when I left the investigation, there was no evidence that concerned me that the foster mum or the foster dad were involved in William's disappearance," Former Detective Gary Jubelin told Sydney's 2GB radio.
Detectives could be close to solving one of Australia's most high profile missing children cases.
On Wednesday, they compared evidence to a Spider-Man suit. It was a false alarm, but they believe although it could take weeks, they will find out what happened to Tyrrell.
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