Can anyone 'PROVE' that it ever was?
EP could do if they were relied on to tell the truth. Seemingly Jeremy was being watched for growing a few weeds,with honest and trusty friend JM making a killing at college selling them,so the police decided to keep a watchful eye on the comings and goings of Jeremy and his massive drug trade.
It was neighbours who'd reported the matter to the police,telling them of JB's activities,so in order that they were believed,the police decided to keep a careful watch on things.
Jeremy himself never believed he was being watched,but then,he wasn't 100% sure was he ?
The only way of knowing this information is from " Taff " Jones's notebook,in which could have been stated,by himself,that Jeremy WAS being watched--------hence " Taffs' " outright conclusion of 4 murders and a suicide. Until then,we're still kept dangling unless some clever dick comes up with the proof that he WASN'T being watched.