enemy action was soon ruled out as the cause of the explosion. experts found the cause to be a british hawkins grenade – a type of anti-tank mine that is detonated when an acid-filled glass ampoule is broken. the device had been placed under the bath chair's cushion. a formal murder investigation was begun. doris brown was interviewed at length at rayleigh police station. it emerged that although archibald brown had been crippled and unable to walk, his will power was undiminished: he harshly ruled his wife and elder son. his wife was not allowed to visit her mother in nearby rochford and archibald brown would constantly ring a bell to get his wife's attention, even if he perceived that a single flower was out of place in a vase. eric brown was constantly beaten and humiliated. doris brown stated that her husband had increasingly appeared to take a dislike to her. eric, too, had noticed the deterioration in archibald's behaviour, but he had taken a liking to his new nurse and their walks together.