British policeman sent to his Death !, page-13

This is most probably correct. But we still don't know who the attacker is. There is some possibility (slight) that it is some other violent type - worked up about Brexit or something. I am thinking of the death of Jo Cox.

The reason I raise this possibility, is that the Westminster attacker had no bomb or gun. If he was a member of ISIS, surely they would have given him a few side arms. They have enough - awash with arms given to them to fight the Syrian govt.