London (CNN) -- A British spy found dead at his home in 2010 -- his naked body padlocked inside a large red carrying bag stowed in the bathtub -- was either suffocated or poisoned, but it is unlikely his death will ever be satisfactorily explained, coroner Fiona Wilcox said Wednesday. Gareth Williams' death was "unnatural and likely to have been criminally mediated," she ruled. He probably entered the bag alive, Wilcox said, reading her ruling to a court around the corner from the home of the world's most famous fictional detective, Sherlock Holmes. But she was sure an unknown person put the bag containing his body into the bath and probably locked it, she said.
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NEW: MI6 chief apologizes "unreservedly" to spy's family for failure to act quickly
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Gareth Williams was poisoned or suffocated in the bag in which he was locked, coroner says
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The bag containing his naked body was put into a bath by an unknown person, coroner rules
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His family calls for an investigation into the secret services' role in the investigation
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