Didnt they see him visiting the actual flat where the terrorists were living?
I havent said it was right what the police did, but they have a decision to make based on the evidence they had at that time.
No, an officer on surveillance made a huge error and wrongly identified poor JdM as the terrorist suspect the police were watching. JdM was not the suspect, Andrea. I don't believe he was ever seen visiting a terrorist's home. He wasn't a terrorist. He was just an ordinary person, minding his own business and living his life just as you or I do. JdM could have been any one of us.
As far as I recall, I believe the surveillance team was short staffed and under pressure, officers were at times working alone, which meant if they went to the toilet no one would be watching for the suspect. So the surveillance team could not do their job properly and this led to panic at times and errors in identification.