Plot discussion (spoilers)

The ending is ambiguous. Did Sandra Kittering kill her husband, Buck? Was Bill Fosdyke murdered?

Buck Kittering could have been killed by accident, since earlier in the film someone says lorries are always hitting people.

We know Sandra sent the English couple to spy on Molly in Urbino and report back the whereabouts of Buck. But why would Sandra want to kill him? It could been because Buck may have killed Bill Fosdyke/Fixit, who may have been Sandra's lover. But Sandra is Italian, and we have been told that Italian women appreciate it when their husbands get murderously jealous.

So maybe she killed him over the water corruption scheme, which we know Sandra is running now. But why would Sandra have to kill Buck over the water scheme? Unless Buck was careless in exposing his power to shut off water by emptying the pool at Fosdyke’s house to make his death seem accidental.

I wonder if reading the book gives any more definite answers to these questions.

Please let me know if I am missing some important clue in the movie that ties things up better.