6 March 1990
“Other enquiry” i.e. not evidentially significant
According to Williamson’s memo of 16 March 1990 to the SIO another of the “other enquiries” that was carried out was a visit to Prestwick Circuits, Ayr (PCB manufacturers) on 6 March 1990. Excellent co-operation and advice was apparently received during discussions with senior management and technicians, and their conclusions were that the board had been professionally manufactured but not to a high standard and using dated technology.
They suggested the best line of enquiry to be that the tin which was used as an etch resist (i.e. that coated the circuit board tracks) was uncommon as was the 9 layers of glass cloth, so these were the best avenues to pursue.
Harrower’s defence precognition demonstrates that he did not have a good memory of the various places that he visited when enquiring into the source of the fragment. However, he did mention that Prestwick Circuits rang a bell.