in the US before 1965, and after a couple of unintentional poisoning, it was banned as household product (see quote). Other countries are still using it to kill rat and ant including China, so why it had to be a foul play? I am just
asking the question, as I don't take side.
Rusyniak DE, Furbee RB, Kirk MA. Thallium and arsenic poisoning in a small midwestern town. Ann Emerg Med. Mar 2002;39(3):307-11.