The Hanging

[TranquillityBase]

 as I read it, realized he drowned himself, the hanging came later.

That was my thought too, but then, why mention the scarf?

The scarf has to be there for him to be hung by the snag/the river.  That's how it became a "hanging".  Leastwise that was my understanding.  That was one of the interesting surprises of the poem, for me.  I began reading thinking he was going to hang himself, but he didn't!  Voila!