Locked Book in Malabal Tor?

OKeeffe

I've stumbled upon a "locked book" at an abandoned camp near the Valeguard Wayshrine that suggests there's a journal that lets you unlock it. Any idea where I find this? The only thing I've been able to find online just says "find a body by the river" but there's a lot of river and the only body I've come across so far was useless.

Edit: Found him. For future reference, he is on the bank where the river converges into a fall directly west of Sleepy Senche Overlook.