A few years ago, we had landscaping done. Once everything was planted, the landscaper took us driving on the country roads to gather pretty stones and rocks. At that time, we wondered about trespassing onto a farmer's field, even though the rocks were close to the road, but the landscaper told us it would not be a problem, as the farmers like to be rid of them.
After viewing the rocks at the crime scene in the picture, along with the seclusion of the area, IMO, if MTR worked at landscaping in the surrounding areas, he may have been very familiar with this road for collecting rocks for landscaping jobs he may have worked on.
Originally, I was of the opinion there were a few rocks that MTR and TLM had to walk around and find, but this is obviously not the case here. Rocks were quite plentiful in all sizes, it would appear.
IMO