The first police officer on the scene is now seriously ill.
Latest news is we now know it was a nerve agent used and they tend to be used by States or sometimes terrorist groups! In case you hadn't guessed they were deliberately targeted. Hundreds of officers are now involved.
^ A 'nerve agent' is normally sprayed onto the victim. So just a minute particle of the spray would be enough to make anyone trying to help the victim ill. Just touching the victim is enough , nerve agents are spread by skin contact. Which is why the emergency services were wearing full BioHazard gear but the police officer was not.