Another chapter has been added to the dismal legacy of America’s involvement in Iraq. An investigation by C.J. Chivers, published in The Times on Wednesday, found that American and American-trained Iraqi troops discovered thousands of abandoned and highly dangerous chemical weapons left over from the rule of Saddam Hussein. These weapons, found from 2004 to 2011, wounded troops from both armies. There are now fears that some could fall into the hands of fighters for the Islamic State, which now controls much of the territory where the weapons were found.

These weapons are not the chemical and biological weapons of mass destruction that the George W. Bush administration claimed as the excuse for embarking on the Iraq war and that, it turned out, did not exist. Instead, they are aged remnants left over from an earlier chemical weapons program in the late-1970s and 1980s that was shut down in 1991. Mr. Hussein used the weapons against Iran in a war from 1980-88.

The investigation exposes shocking failings by the Pentagon, among them a callous disregard for the safety and care of American and Iraqi troops and a disturbing pattern of secrecy that can only erode public confidence in government.

Based on extensive interviews and documents obtained under the Freedom of Information Act, the report said that about 5,000 chemical warheads, shells or aviation bombs were found. On six occasions, soldiers suffered wounds; at least 20 American troops and seven Iraqi police officers were exposed to nerve or mustard agents.