Truck driver Peter Bashkurt was tasked with collecting an excavator from a property near where the three-year-old vanished in 2014.
The toddler - who was last seen wearing a Spider-Man costume - went missing while playing on the verandah at his foster grandmother's home in Kendall, on the NSW mid-north coast, on September 12 that year.
Gary Jubelin who previously investigated William's disappearance was in the packed courtroom. (Dan Himbrechts/AAP PHOTOS)
As an inquest into his disappearance continued on Wednesday, Mr Bashkurt said he had seen a short, overweight, blonde woman park her jet-black Toyota Camry in front of him at a long-distance bus stop in Kew, not far from Kendall.
The 64-year-old said he again saw the vehicle park in front of his Kenworth prime mover as he was waiting in front of the op shop in Kendall about 20 minutes later.
"You had been in Kendall that day and you had seen a car that you thought was acting suspiciously?" counsel assisting Gerard Craddock SC asked.
"Correct," Mr Bashkurt replied.
Something must have "triggered" the woman to make her park in front of his vehicle, he told the court.
"Why would she be there killing time and eventually turning up at the location where I was?" the truck driver asked.
"What was her purpose? I have no idea."
After he picked up the excavator, he said he saw a grey dual-cab ute loaded with tools and a 5-series BMW coming towards him on Batar Creek Road - the location of later police searches for William or his remains.
The truckie testified about car movements in the area where police later searched for William. (Shane Chalker/AAP PHOTOS)
But neither vehicle turned out of the road where the toddler's foster grandmother lived, the truck driver said.
Mr Bashkurt gave evidence by video link from his home, occasionally halting his evidence to yell at his barking dog.
The courtroom was packed with supporters of the foster parents, journalists, court-watchers, and current and former police officers.
They included prominent ex-homicide detective Gary Jubelin, who was involved in investigating William's disappearance until he was replaced on the case.
The current round of inquest hearings, which began on Monday, has focused on a police theory the foster mother, who cannot be legally named, disposed of the toddler's body after his accidental death on the Kendall property.
She allegedly loaded the body into her own mother's grey Mazda and concealed it before calling triple zero out of fear another child under her care would be taken away, Lidcombe Coroners Court was previously told.
William Tyrrell's foster mother (right) has denied any involvement in his disappearance. (Dan Himbrechts/AAP PHOTOS)
The foster mother has consistently denied any involvement in William's disappearance.
After Mr Bashkurt's evidence, the court was closed as the coroner viewed two electronically recorded police interviews from 2014 and 2022 involving another key witness, who cannot be named or identified.
A four-hour grilling of the foster mother before the NSW Crime Commission will be played on Thursday before the inquest comes to a close.
No one has been charged over William's disappearance and a $1 million reward for information stands.
Despite a decade-long investigation involving hundreds of persons of interest and dozens of searches, no trace of the boy has been found.
