So in my dim and distant past I had a spate of knicker and occasional sock thievery over the summer months.
The mystery was eventually solved when I caught the fuzzy feline assailant in the act of underwear abduction. He was then traced back to a house in the next street.
From henceforth a arrangement was made whereby myself and my other neighbour would pop round and reacquaint ourselves with our underwear from a box the cats owner kept for his cats kleptomanical fetishy escapades.
This arrangement sufficed until fetishy cat and his owner moved house. The years since then have been filled with a happy absence of liberated frillies.
Till today's perturbing discovery, whilst chopping mushrooms and gazing out the window I noticed that the current rear neighbours have pulled down all the trellis and vines. This in turn reveals a tall luxuriant abundant growth of pampas grass. 
Clearly my previous neighbour was actually a huge pervy hairy swinger with a carefully trained cat knicker thief that brought home various knickers for him to wear during his seedy orgies in his semi detached bungalow, before washing them and putting them in his box.
AIBU to make this conclusion purely on the chance discovery of some unexpected flora many years later?