A special inquiry resumes on Friday to continue examining several police strike forces formed to investigate suspected hate crimes between 1970 and 2010.
Mr Willing last took the stand in the royal commission-style inquiry in February, where he was questioned over two days about Strike Force Neiwand's examination of more than 50 suspects involved in the murders of three gay men in the 1980s.
The former top cop will be quizzed about the death of slain American mathematician Scott Johnson, whose 1988 death was initially ruled a suicide before the case was reopened in 2012 following pressure from his family.
A coroner in 2017 determined the matter involved human intervention and in February Scott White pleaded guilty to Mr Johnson's manslaughter in the NSW Supreme Court.
Mr Willing will be questioned over his team's responsibility to properly investigate Mr Johnson's death, including whether police turned a blind eye to several suspects.
The inquiry is also set to explore former detective Pamela Young's controversial interview on ABC Lateline in 2015, where she told the program Mr Johnson likely took his own life, while investigations were ongoing.
Former NSW police officer Duncan McNab says the inquiry's work is imperative and important.
"These inquiries stimulate the memories of people who might just know that little bit and who finally grow a spine after being too scared to come forward," he said.
"But it's a bit like musical chairs at this stage, no one wants to take responsibility for what was actually a complete screw-up."
With documents still being sought and hearings expected to run into June, NSW Supreme Court Justice John Sackar has been granted a two-month extension to deliver his findings by August 30.
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