What was the cause of Conchetta Pignati's death in The Pigman, and where did she die?

Conchetta Pignati, Mr. Angelo Pignati's wife, was the love
of the Pigman's life. The two had shared a love of gourmet food, jokes, and wine. He
misses her tremendously and mourns her still. His love is evident in
chapter ten:

"We loved each other. We didn't need anyone
else. She did everything for me. We were each others life," he managed to say, and then
broke into sobs."

He misses her so much that, at first, he
tells Lorraine and John that his wife is on holiday in California. It isn't until the
kids stumble upon her death records that they know the truth. They ask Mr. Pignati about
the truth, and he finally confesses. She is dead.

The cause
of Conchetta's death is never really explicitly stated. One time, Mr. Pignati asks the
kids to play a game with him where he tells a story about an adulterous wife being that
is murdered by an assassin, and the kids are asked to figure out whom the assassin was.
However, although this makes John and Lorraine question how Conchetta died, if she
was the audulterous wife that was murdered, and whom she may have been mudered by, we
really cannot assume that she was assassinated, and we certainly cannot assume that Mr.
Pignati killed her, so her death remains a mystery.