slime

lima

peittää limaan Soft, moist earth or clay, having an adhesive quality; viscous mud; any substance of a dirty nature, that is moist, soft, and adhesive; bitumen; mud containing metallic ore, obtained in the preparatory dressing.
Shakespeare

As it the Nile ebbs, the seedsman / Upon the slime and ooze scatters his grain.

If this guy knows who killed Robert, the right thing to do is to tell the police. If he doesn't know, really, then he's an opportunistic slime. It's still blackmail.

th'eternall Lord in fleshly slime / Enwombed was, from wretched Adams line / To purge away the guilt of sinfull crime ....

And they said one to another, Go to, let us make brick, and burn them thoroughly. And they had brick for stone, and slime had they for morter.