I just finished reading Ann Rules' book Green River, Running Red. Her take on the Green River Killer investigation. In her book, she mentioned several times how he passed not one, but two polygraphs. I did learn something though. It appears the polygraphs were given after he killed all the prostitutes, not during his killing spree. It is also clear that he was discarded as a suspect, although one investigator, Matt Haney really felt he was the killer.
A misplaced reliance on the polygraph if there ever was one.
For earlier discussion of the role of polygraphy in the Green River Killer investigation, see Gary Leon Ridgway, Deadliest Serial Killer in U.S. History, Passed Polygraph and Killed Again (https://antipolygraph.org/forum/index.php?topic=1436.msg11312#msg11312).