The Man Beast (Side Quest)
A side quest just northwest of Krokodilopolis, in Faiyum Oasis.
Wander by the marker to overhear tales of the Man Beast.
Go over and investigate. There are several things to check out, but the plot-advancer is the little collection of limbs by the waterline.
Bayek says he can't tell whether they're human, but they're pretty clearly human. In any case, scan with Senu to locate the source, east across the river.
Cross the river and enter the indicated cave. The apparent dead end means, of course, that there's an underwater tunnel here.
It runs straight east, and comes up in a furnished crocodile pit, complete with crocodile. Defeat it so you can get a closer look at all the corpses.
Exit the water (alas, none of your trinkets include soap), and free the prisoner in the cage to your right.
He'll finger the monster responsible for all this. Loot the area (there are some interesting documents about), then exit, either the way you came, or the ladder up to street level.
Your target will be in the market with his single guard, likely taking in a show at the public stage.
There is a protruding bit of timber here custom made for assassination. Not the most private venue for a murder, but needs must.
His death completes the mission. Presumably the gossips back on the island will hear about their creepy neighbor's exoneration in time.