I'm not really following. If you're talking about the Canton PD, which was much earlier in the morning, there was only a dusting on John's body, according to testimony and only a few inches on the ground. They brought out a leaf blower and should have found taillight if it was there. They only found some glass, which arguably should have been way harder to see.
The sallyport garage was much later. Much more snow then. There was was a period of time after the car was brought to the sallyport that the lawn was totally unsecured. Proctor also lied about the time frames involved with retrieving the car in Dighton.