That's pretty sick. Probably some *ssh*le with some pretty deep problems!!
There are several unsolved dog poisonings in the Greater Toronto area. In 2004 somebody left hotdogs laced with anti-freeze in an off leash dog park in the east end of the city. Several dogs died lingering painful deaths. A couple of months ago someone else left some white powdery substance in another dog park in Oakville to the west of us. Several dogs got sick but I can't remember if any of them died.
What's worse is within the last 2 weeks some sick SOB left razorblades in a park used by disabled kids in Hamilton. Fortunately they were discovered before any of the kids got hurt.