Many Western nations have experienced significant declines in crime in recent decades, but could the removal of lead from petrol explain that?
Working away in his laboratory in 1921, Thomas Midgley wanted to fuel a brighter tomorrow. He created tetraethyl lead - a compound that would make car engines more efficient than ever.
But did the lead that we added to our petrol do something so much worse? Was it the cause of a decades-long crime wave that is only now abating as the poisonous element is removed from our environment?
If you want to understand the causes of crime - and be tough on them - you need to start with lead, says Dr Bernard Gesch, a physiologist at Oxford University who has studied the effect of diet and other environmental factors on criminals.