After the invasion, the Iraq Survey Group (ISG), headed by American David Kay, was tasked with searching for weapons of mass destruction. The survey ultimately concluded that Iraqi production of weapons of mass destruction ceased and all major stockpiles were destroyed in 1991 when economic sanctions were imposed, but that the expertise to restart production once sanctions were lifted was preserved. The group also concluded that Iraq continued developing long range missiles proscribed by the U.N. until just before the 2003 invasion.