Well, I'm not sure if this thread is about Benghazi or WMD's but there were no WMD's in Iraq when we invaded because Saddam destroyed them all.
After the invasion of Iraq in 2003, the Bush administration formed the Iraq Survey Group and tasked it with the job of locating WMD stockpiles in Iraq. The ISG was staffed with hundreds of intelligence analysts and military personnel from the United States, the United Kingdom and Australia. The group scoured Iraq, searching for deposits of weapons.
After nearly two years of investigation, the ISG concluded that:
"Saddam Husayn ended the nuclear program in 1991 following the Gulf war. ISG found no evidence to suggest concerted efforts to restart the program."
"While a small number of old, abandoned chemical munitions have been discovered, ISG judges that Iraq unilaterally destroyed its undeclared chemical weapons stockpile in 1991. There are no credible indications that Baghdad resumed production of chemical munitions thereafter."
"In practical terms, with the destruction of the Al Hakam facility, Iraq abandoned its ambition to obtain advanced BW [biological warfare] weapons quickly. ISG found no direct evidence that Iraq, after 1996, had plans for a new BW program or was conducting BW-specific work for military purposes."
Experts from the three nations failed to document any existent biological or nuclear weapons and discovered only a few random chemical weapons. The ISG concluded that contrary to what most of the world had believed, Iraq had abandoned attempts to produce WMDs. In his congressional testimony, the head of the ISG, Charles Duelfer, admitted, "We were almost all wrong" on Iraq.
The ISG report was sufficient to convince the Bush administration that there were no WMDs to be found; they called off the search in 2005.
FactCheck.org : No WMDs in Iraq