The case of the rock, the lady in the lake and a dubious murderer

In 1997 some amateur divers discovered at the bottom of Coniston Water, a lake in the British Lake District, a corpse. The body of a women was wrapped up in plastic bags and tubs of lead have been used as weights to hide it in the  24m deep water.
The woman was identified as Carol Ann Park, disappeared in the year 1976. An autopsy revealed that Ann Park was killed with an ice pick and soon her ex-husband, Gordon Park, was suspected and arrested. The press publicized this crime with the title of "The Lady in the Lake Murder".

However there was no hard evidence against him, only a supposed confession by Park to a cell inmate during the imprisonment on remand, so he was soon released. 

In 2004 Park was rearrested, based on new evidence: a rock. A rock, assumed to have been used also as weight in the plastic bag, and found near the corpse was similar to rocks used by park to build a wall of the family's bungalow. Prosecution's expert and geologist Duncan Pirrie concluded that there were no naturally occurring outcrops on the shores of the lake of this kind of rock, the only possible source was therefore Park's home.
However the defence of Park commissioned two geologists, Kenneth Pye and later Andrew Moncrief, to disprove this important evidence that connected Park to the corpse. Pye studied the rock and his results were astounding. The rock was a sample of Westmorland green slate - a metamorphic tuffaceous sandstone - lithology part of the Borrowdale Volcanic Group not present near Coniston Water, but found in the central parts of the Lake District.
The boulders in the lake, so the final verdict of the two geologists, were of glacial origin, transported during the last glacial maximum from the Cumbrian Mountains to the area of the lake. Glacial till was therefore widespread on the bottom of the lake, the shores and the entire landscape - so were rocks of green slate. The supposed unique connection between Park and the site of discovery of the corpse was disproved by the general geology and galcial origin of the lake.

Despite this devastating setback for the prosecution, the trial, based mainly on circumstantial evidence, ended with a prison sentence for Park.
The judge commented the geological dispute about the origin of the particular rock as follows:

"Rocks, ladies and gentlemen, therefore rocks…[] The science, underlying this research was exceptionally challenging, not true? It was of awe-inspiring quality that none of us has ever been enjoyed…[]… I think the experts managed to formulate their opinions in an understandable way. At least the important facts have become clear, we have understood in which final statements both researchers disagree."