It was a sky news tweet. Looking at the news site now the back pack WOMD may have contained nails. When did it become possible to buy WOMD components from B&Q? Feels like this story may have been exaggerated a little by reporters or the police?
The Boston bomber was charged and found guilty of various counts of using a Weapon of Mass Destruction. WoMDs cover any type of explosive device under US law.
I remember watching a programme on TV I think it was catfish where a guy had been convicted of having a weapon of mass destruction. He was carrying a sawn off shotgun between states. Legal in one state not in the other.