The Metropolitan Police's Deputy Assistant Commissioner Martin Hewitt said they are trying to "trace unidentified DNA" to understand what happened to Gareth Williams.
He added that the case "remains a current investigation".
Following an inquest, a coroner can return a 'narrative verdict'. This is a factual statement of the circumstances surrounding someone's death, without attributing the cause to an individual. Narrative verdicts have been an option for coroners in England and Wales since 2004.
DCI Jackie Sebire has said that new lines of inquiry had come to light during Gareth Williams' inquest and that the investigation into his death is continuing.
In a statement delivered by solicitor Robyn Williams, the family of Gareth Williams said their grief was exacerbated by the failure of Gareth's employers, MI6.
Speaking on behalf of the Williams family, solicitor Robyn Williams said: "Our grief is exacerbated by the failure of his employers at MI6 to take even the most basic inquiries as to his whereabouts and welfare, which any reasonable employer would have taken."
He said the Williams family were "extremely disappointed" over the failure of MI6 to make relevant information available and asked for the Metropolitan Police to review how the investigation will proceed.
He added: "Gareth always was and always will be a special and adored son and brother.
"We miss him every single day and cannot describe the depth of the sorrow his absence leaves in our lives. We love you Gareth and will treasure your memory eternally. To live on in the hearts of those we love and leave behind is not to die."
One of Britain's most senior spies apologised to Gareth Williams' family today for the mix-up which saw MI6 fail to report his disappearance for a week.
Sir John Sawers, chief of the Secret Intelligence Service, expressed the "deepest condolences" of MI6 and GCHQ for the death.
In a statement delivered by MI6 lawyer Andrew O'Connor, Sir John said the service should have acted more swiftly when Mr Williams failed to turn up to work in August 2010.
Mr O'Connor said: "On behalf of the whole organisation, Sir John regrets this deeply and apologises unreservedly."
ITV News correspondent Paul Davies explores the theories surrounding the death of MI6 code-breaker Gareth Williams.
Please do not attempt to recreate the demonstration contained in the video.
Mr Williams' decomposing naked body was discovered padlocked inside a holdall in his flat in August 2010. Today coroner Dr Fiona Wilcox delivered a narrative verdict, stating it is "very unlikely" the mystery will ever be explained.
On the balance of probabilities, the Coroner agrees with Mr Williams' family that Gareth was unlawfully killed - though that's not the actual verdict.
Dr Fiona Wilcox thanks DCI Jackie Sebire, who is leading police inquiry, and gives her sympathies to Gareth's family.
Coroner Dr Fiona Wilcox says she's satisfied the bag was placed in bath by a third party, probably to conceal the decay of body and leakage.
She adds it's "beyond belief" Gareth could have arranged the lock and zips so neatly from the inside.
The coroner says Gareth Williams' death was caused by an "unnatural cause" but she added that she could not be "satisfied so that I'm sure that he was ... unlawfully killed".