Who was the assassin in "The Assassin and the Boatman" in "The Pigman"? Is he the one who killed the wife?

The story
of "The Assassin and the Boatman" that Mr. Pignati tells goes like
this:

A wife lives with her husband at one side of a river.  She has a lover
who lives at the other side of the bridge.  One night, her husband goes away on business and
refuses to take her with him.  She spends the night at the lover's house.  In the morning, she
tries to walk across the bridge to go home before her husband gets there, but sees an assassin
at the other side of the bridge, waiting with a knife.  She begs a boatman to take her across
the river at a different spot, but he refuses because she has no money.  She asks the lover for
help, but he insists it is her own problem.  She finally runs across the bridge in a panic, and
is killed by the assassin.

So the assassin is the person who kills the wife,
but the point of the story is to figure out who you think is most responsible for her death.  Is
it the assassin, her husband, her lover, the boatman, or herself?