I can accept that once the police chief had tried to defect and the stories of Heywood's death being suspicious began to circulate that Bo's political enemies began sharpening their knives for the kill. But it doesn't explain why in the 3 year period starting in 2009 when he is reported to have first met the MI6 officer to his death in 2012 the Chinese security services did nothing to prevent Heywood from providing sensitive information to the British Government. You'd therefore have to accept that either the information he was providing wasn't of a sensitive nature or the Chinese security service is completely incompetent.