The difficulties homicide detectives face investigating any suspicious death of a secret intelligence service officer came under intense scrutiny during the Gareth Williams inquest.
Fears of risk to national security or individual witnesses force Scotland Yard to operate at arm's length when dealing with MI6 and GCHQ.
Once the body is identified as an operational Secret Intelligence Service (SIS) officer, different rules come into play.
Detective Chief Inspector Jackie Sebire, senior investigating officer in the Williams case, and her team were allowed no direct access to sensitive witnesses or evidence. Instead, security-cleared officers from SO15 – counter-terrorism – acted as go-betweens.
So, SO15 officers, not those from homicide command, interviewed SIS witnesses, in the presence of their line managers and legal representatives, and put the questions murder detectives would rather have put themselves.
Then instead of producing signed, sworn, verbatim statements, SO15 produced "anonymised" notes, drawn up after interview.
It is not "impossible" to get a homicide detective vetted and cleared to question SIS, but it would take time and is not the normal procedure adopted.
Sebire admitted homicide would have liked "primary access". She added: "That simply wasn't possible in those circumstances. "Given the circumstances, this was the best possible scenario". She had faith in the SO15 officers deployed to assist, the inquest heard.
Difficulties, however, were apparent.
Not until the penultimate day of the inquest was Sebire made aware that potential evidence, namely nine assorted memory sticks and a black holdall found at Williams's office at MI6 HQ in Vauxhall, central London, even existed.
She was not given an inventory of items and documents found in Williams's shared locker, or in a locked North Face bag under his desk, because none was drawn up due to the "sensitive nature" of some of the contents.
The MI6 offices had been searched by the SO15 forensic officer Detective Constable Colin Hall, under the leadership of SO15 Detective Superintendent Michael Broster, accompanied by two SIS officers.
Sebire said she would "have expected to have been told" about this potential evidence, "so we can review It and assess its value".
Throughout the inquest, the Williams family lawyer, Anthony O'Toole, was critical of the way the investigation was being handled. S015, he said, simply took assurances from SIS without questioning.
There were "errors" and "discrepancies" in the anonymised statements, which he described almost like "attendance notes", and no SIS officers had been given the notes to review or check for accuracy, he said.
"It was almost under the Old Boys' Act," he said to Broster of assurances given by SIS. "They told you that and you accepted it."
