Death of MI6 spy Williams, whose body was in a padlocked sports bag, was probably an accident.

[Spider Jerusalem]

10. Only if whoever did it knew of his proclivities.

Otherwise it's kind of unlikely. And given that he apparently had a penchant for self-bondage and being confined in tight spaces, that he did it himself and couldn't get out again seems rather the most likely explanation. He had previous with getting himself into situations he couldn't get out of:

In a statement read out earlier, Mr Williams' former landlady in Cheltenham said she once found him lying in his boxer shorts tied to his bedstead, in what she thought was a "sexually motivated" act.

Jennifer Elliot said he had shouted for help because he was unable to untie himself.

She said he claimed he wanted to see if he could free himself, but both she and her husband thought it was sexually motivated rather than an act of escapology.

He had been lying on his back with both hands and arms tied and was "very embarrassed and apologetic" after being cut free.

http://www.bbc.co.uk/news/uk-17837869