[He minded the directions he was given, approaching the stone to inspect it. He delicately picked for a moment at the moss upon the stones, not peeling any of it away but rather taking stock of the condition and what there was.]

It has been left for quite a long time... A sponge should do well... A natural one, it is just rough enough to work away the moss and dirt without damaging the stone itself. The whole stone should be doused in purified water and allowed to soak in first. ... Several times, perhaps.

It will take some time, to restore it to an acceptable state.

[No, no questions as to why precisely these stones mattered, no question as to what motivated the man, but rather a different one:]

What happened to the shattered stones?