but he was not a formal mi5 subject of interest. more than three days into this investigation, counter—terrorism detectives do have a potential motive for the killing, islamist extremism and a desire to kill a british politician, but it is still not clear why sir david amess in particular was targeted. counter—terrorism command searches of three properties in london linked to ali harbi ali are now over. this flat in a north london town house was a hive of police activity yesterday, but today it was quiet. it seems that the investigation of the murder of sir david amess is not expanding, but remains focused on the man arrested at the scene. the suspect is still being questioned at a police station in london. he has not yet been charged with any offences. daniel sandford, bbc news, new scotland yard. to westminster and our political editor laura kuenssberg.