In the Percy case, the first cop to investigate the backyard saw footprints in the dew that went down the bluff in a southerly direction. They continued in the sand, in the same direction, until they disappeared into the water. The bayonet was found about 700 feet down the beach in the direction of the footprints, and about 40 feet out, or as they said about as far as someone could throw it. You have to keep in mind that Kenilworth, Illinois was in those days (and may still be) like the 3rd richest community in the country. The scenario of someone walking around there at 5 a.m. on a Sunday morning with a bayonet would seem to scream crazy. I grew up a mile from there. I know people who have places on that beach. They said in the mid sixties those beaches were always being crashed by area kids (big families back then.) This happened at the tail end of summer. The idea that this knife, which is in the huge category, matched wounds found on the victim, and would have been sitting out there just 40 feet out and four feet down, in the direction of those footprints, in that kind of town for very long with all of those kids using those beaches, in that kind of community, at that time of year...seems remote. No prints and blood (would have obviously been gone after three days in the lake) but it seems the cops (and Coast Guard) were searching with such determination because they were pretty sure they were going to find something relevant. I think it's pretty clear they did. Such a knife being used in the Zodiac attack is interesting as the suspect had ties to Percy's neighborhood and the Bay Area, was a suspect in several murders, was crazy and violent (see bayonet carrying offender in Kenilworth at 5 a.m. on a Sunday), obsessed with military weaponry, and for such a knife to be used to attack someone in a place like Kenilworth or Lake Berryessa (if not anywhere else outside of a battlefield or military base) would be all but unheard of.