A serious WTF?

Officials in Huntsville Texas are reporting that razor blades were found embedded in children's equipment at two parks in the city. The sabotage was discovered by City workers on July 6th and there have been no reports of injuries associated with the incidents.
This is a head scratcher for me, do they inspect the equipment every day, or is there a schedule for such inspections? On the surface, it is either a miracle that no child was injured, or parents were tipped off to keep kids away. The incidents happened at Emancipation Park on Martin Luther King, and Boettcher Mill Park on Boettcher Mill Rd. They  are approximately a mile apart, with the Huntsville unit roughly in the middle.
Whether pure luck or pure BS, this is pure evil.
*update*

There was also an incident in Festus MO where razor blades were found on shopping carts at Walmart. My initial suspicion is that they are too close together to be a copy cat, so possibly a coordinated attack? One person was hurt in Festus, store personnel found a second cart.