London (CNN) -- Gareth Williams, the MI6 codebreaker found dead inside an externally locked bag in his apartment in 2010, was probably not killed as previously believed, London's Metropolitan Police said Wednesday, citing a lack of evidence otherwise.
Taking a different position from a coroner's report last year that said it was likely someone killed Gareth Williams, London's Metropolitan Police said its three-year investigation suggested that Williams most likely locked himself inside the large bag.
"We believe that it is a more probable conclusion that there was no other person present when Gareth died," Deputy Assistant Commissioner Martin Hewitt said.
But the Met said that despite its investigation, there remained insufficient evidence to be definitive on how Williams died.
"There are holes in what we understand about the circumstances of Gareth Williams' death," Hewitt said, admitting that some of the evidence is "odd."
This includes the lack of Williams' DNA on the padlock used to lock the large red bag his body was found in and the lack of hand prints on the edge of the bath where it was found, he said.
"What we are left with is either individual pieces of evidence, or a lack of such evidence, that can logically support one of a number of hypotheses," Hewitt said.
The case has gripped the British public since Williams, known for his mathematical genius and code-breaking talent, was found dead at age 31 in August 2010.
Among the theories aired by UK media were that Williams might have died at the hands of foreign intelligence agents or as a result of a kinky sexual encounter gone wrong. Added to that speculation was the discovery of women's clothes, wigs and cosmetics in Williams' apartment.
At the inquest into his death last year, coroner Fiona Wilcox shot down that speculation, saying she thought Williams bought them out of an interest in fashion, rather than any sexual motivation.
Other reports about the "body-in-a-bag spy" detailed how two experts spent days trying to figure out whether Williams could have contorted himself in such a way as to lock himself into the North Face holdall bag, with a key to the padlock inside.
Video of two experts trying to recreate the scene was showing to the court. One had tried 300 times without success, but neither ruled out definitively the possibility Williams could have somehow done it alone.
"It is now proven that it is theoretically possible for a person to lock themselves in that exact holdall, with the same type of lock, and in the configuration in which Gareth was found. It is important to note that this fact was found to be a possibility by the inquest," Hewitt said.
Meanwhile, family members suggested Williams had been murdered by killers versed in the "dark arts" of espionage.
Referring to speculation that Williams' flat might have been forensically cleaned by unknown people responsible for his death, Hewitt said Wednesday that a deep-clean would have removed all traces of Williams' DNA as well that of visitors to his flat.
He said 10 to 15 traces of DNA had been found that were too insignificant to use to build a full profile and said advances in forensic science could "present opportunities for progress." For the time being, however, there are "no active lines of enquiry that it is proportionate to pursue."
Williams' family expressed their regret that mystery still surrounds his death but said they agree with the coroner's verdict "on the basis of the facts at present known."
"We are naturally disappointed that it is still not possible to state with certainty how Gareth died and the fact that the circumstances of his death are still unknown adds to our grief," they said in a written statement.
The family reiterated their disappointment that Williams' employers at MI6 had not checked on his welfare when he failed to attend work on August 16, 2010.
Williams was finally reported missing by a co-worker on August 23, more than a week after the normally punctilious employee had last shown up at work.
"We believe that if proper steps had been taken in the same manner as any reasonable employer would have undertaken, further information relating to the cause of his death might have become apparent and not have been lost due to the length of time before Gareth's body was found," they said.
The family also noted that the Met's investigators "were at last able to interview directly members of (UK intelligence agencies) GCHQ and SIS."
Addressing media, Hewitt disputed a suggestion that police had been "blindsided" in their investigation by intelligence agencies but acknowledged that their method of interaction had improved during the investigation. "We didn't get it right at the beginning," he said.
Initially, he said, the only Met officers to deal with the intelligence agencies were those in SO15 -- or counterterrorism command. The SO15 officers had assessed Williams' vetting and personnel files and found nothing relevant to the case.
After the inquest, the senior investigating officer in the case personally requested and was granted access to the files and came to the same conclusion, Hewitt said.
"The investigation into Gareth's death will remain under review, and any new significant information or evidence will be robustly investigated," he said.
"If it is possible for us to give his family more answers we will do so."