The Chronology of PT/35(b): 23 May 1990

23 May 1990

According to their HOLMES statements, Williamson (BS) and Langford-Johnson
(S1983GJ) went back to Ferranti by appointment, and a further examination of
PT/35(b), DP/11 and DP/31 was carried out by Allan Worroll, who removed solder
mask from the backside of DP/31 by means of a grinding machine, to allow further
analysis of the fibreglass construction. Worroll’s HOLMES statement confirms that
he removed the solder mask on the reverse side of the fragment to reveal the uncoated
fibreglass laminate, to allow the most thorough examination of the resin from the
laminate. L-J in evidence stated that he was present when Worroll removed the solder
mask from the reverse side of DP/31 to the tracks. In his ch10 CP Worroll examined
DP/31 but had no memory of it, could not remember having seen it or examined it,
although he noted he had signed the label. He stated that he had no reason to doubt
the officers who were present, if they were to say he had carried out an examination
of DP/31. A PF’s note on the precognition explains that Worroll does not remember
grinding down DP/31, but that L-J’s notebook recorded this and it had been lodged as
a production. [Note also the scientific examinations of DP/31 and PT/35(b) in 1999
by Dr Reeves and by the Dundee Uni experts, which seem to confirm that the former
had been cut from the latter.]

DP-32 Page 1

DP-32 Page 1

The same day the two officers and Worroll met Dr David Johnson at Manchester
Uni’s Department of Science and Technology, after prior arrangement. According to
Worroll’s HOLMES statement this was done after direct contact between the police
and Dr Johnston, at Worroll’s suggestion. The purpose was to carry out a comparison
between the fragment and two samples of fibreglass laminate which John French at
Ciba Geigy had said closest matched the fragment, of the 23 samples he had been
given. The two samples were Ditron and Sefolam. According to the police officers’
statements another test was also carried out to allow Worroll to assess more clearly
the reason for application of a coating of tin to the copper conducting tracks.

According to his HOLMES statement Dr Johnston carried out an analysis of the
surface chemistry of the fragment (it does not specifically refer to DP/31 as the
fragment that was tested) using secondary ion mass spectrometry. After this he stated
that the fragment was not identical in composition to either of the samples. He also
stated that his analysis would assess the surface chemistry of the conducting tracks to
see if they consisted of pure tin or tin containing any other species. There is no
mention in the HOLMES statements of Williamson, L-J, Worroll or Johnston of the
results of this latter analysis. The officers’ statements mention that Johnston later
provided a full analysis report, labelled DP/36 (prod 345). Johnston’s own statement
dates the provision of this report as 4 June 1990, but although the report is dated then,
the police label attached to it suggests it was received by post on 11 June 1990. The
report is mainly in scientific jargon. The report might indicate that lead was detected
on the surface tracks of the fragment, as well as tin (see p6-7 of the report – pb is the
chemical symbol for lead; sn is the symbol for tin); however, this would be
inconsistent with Worroll’s description, which he gave the day after Johnson did the
tests (see 24 May 1990, below) where he said the tracks were coated in pure tin; and
with the analysis of Dr Wilkinson, above, that indicated that only tin and copper could
be found on the tracks. Urs Bonfadelli, an employee of Thuring, who made the MST-
13 circuit boards, stated that the tracking was to be in tin, he did not mention lead.
This is consistent with the tracks having been coated in pure tin. Note also that in
1992 Dr Johnson compared PT/35(b)’s results to a similar analysis of a control
sample MST-13 circuit board and concluded that, at its highest, there was nothing in
the results to indicate that the two were different, when considering the results
qualitatively – see under 5 March 1992, below. The report also confirmed that the
fragment did not appear to match the two samples that had been provided (see p1 of
the report).

In his ch10 CP Johnson said Worroll first suggested examining the solder on the
fragment but this was a non-starter as the likely exposure to high temperatures during
the explosion would alter the composition of the solder, so that comparison with any
control samples would be irrelevant, although he stated that it would be different for
the combination of lead and tin in the solder. He then went into details about the
testing he did of the fragment and two control samples. He was shown his report,
DP/36 and noted that he had washed PT/35(b) in heptane, a mild detergent, to remove
surface contaminants from e.g. the plastic bag, from the fragment, but he noted that he
did not wash the two control samples, Sefolam and Dytron, so he said that the
comparative results might not be entirely reliable. He suggested that it would not be
possible to totally exclude a match between the fragment and Sefolam as Sefolam
might have produced a similar result to the fragment, had it also been washed in
heptane, since the main difference between the two was the presence of fluoro
carbons on the Sefolam, which could have been washed off PT/35(b) by the heptane.

In his CP 27/11/99 Williamson was asked if Johnson’s report (DP/36) contained any
images produced by the SIMS, and he said he was certain they did not receive any
such images. In Johnson’s CP he said seemed to indicate that the SIMS images
should have been with his report (although he did not say this explicitly) and he
suggested they would have been in an A5 envelope.

NB Johnson was also seen by police in 1992 and asked to examine a control sample
MST-13 circuit board – see under 5 March 1992, below. NB Worroll and Johnson’s
signatures are visible on the labels for DP/31 and PT/35(b).

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