“Site visits are important opportunities for investigators to review physical evidence, including weapons remnants, impact sites, and forensic evidence. They help investigators understand the extent of harm an attack has caused and what exactly was damaged,” Priyanka Motaparthy of the Human Rights Institute and a co-author of the report, told The Intercept. “Investigations that don’t take into account this type of information risk underestimating the impact of an attack or failing to understand what exactly was hit.”

Most U.S. investigations of alleged civilian casualty incidents never include even one such visit, according to a new analysis of 228 official U.S. military investigations conducted in Afghanistan, Iraq, and Syria between 2002 and 2015. The military conducted site inspections in only 16 percent of the casualty investigations reviewed for the study by researchers from the Center for Civilians in Conflict, or CIVIC, and the Columbia Law School Human Rights Institute, or HRI.

After the attack, a U.S. team conducted two inspections of the strike location. While such site visits might seem an obvious prerequisite for any legitimate investigation into civilian casualties, they’re surprisingly rare.

Everything was done by the book. The target was an enemy stronghold and the strike seemed precise and flawless — except that it wasn’t. Col. Mohammad Shumari , an Iraqi official working in the area, later told CNN that 141 bodies had been removed from the attack site after the American smart bomb detonated explosives stored by ISIS inside the building. The dead included between 137 and 140 civilians, including women and children, according to Isler.

It was the midpoint of a 10-month battle to dislodge the Islamic State from the Iraqi city of Mosul. Two ISIS snipers were holed up in a “defensive fighting position built into the second story of the structure” in the al-Resala district of Mosul’s al-Jadidah neighborhood. Iraqi troops were taking casualties and asked their American allies for help. “At 0824 on 17 March, 2017, in accordance with the applicable rules of engagement and the law of armed conflict, a coalition U.S. aircraft delivered a single GBU-38 precision guided munition against two ISIS snipers,” U.S. Air Force Brig. Gen. Matthew Isler said in the wake of the strike.

“In Search of Answers: U.S. Military Investigations and Civilian Harm” examines U.S. efforts to track, assess, and investigate reports of civilian casualties caused by its forces. The researchers found that while the U.S. military can effectively investigate civilian casualty allegations, its inquiries are often perfunctory and marred by serious deficiencies, if they’re carried out at all.

“Civilians injured in U.S. military attacks, and the families of those who are killed, have endured long and painful struggles trying to find out why they or their loved ones were harmed and whether their communities are still at risk,” said Motaparthy. “They have a right to learn what steps the military has taken to investigate these often devastating losses.”

U.S. standard practice when it comes to collecting testimony may be even more troubling. While U.S. investigators regularly interview military witnesses, they almost totally ignore civilians — victims, survivors, family members, and bystanders — “severely compromising the effectiveness of investigations,” according to the study. U.S. military personnel interviewed civilian witnesses in just 21.5 percent of the investigations covered in the report.

Despite close surveillance of the structure bombed in Mosul in March 2017, Iraqi and U.S. forces said they were unaware that civilians were sheltering there. It took a site visit to find the corpses in the bottom floors of the building and conversations with relatives to identify the dead. An unpublished internal Defense Department study reinforced the importance of such “ground truth,” finding that in 90 percent of the cases analyzed, initial aerial bomb damage assessments in Afghanistan missed civilian casualties that were later identified through investigations by ground forces, according to the CIVIC and HRI report.

The U.S. military ultimately took responsibility for the strike that led to the bloodbath in Mosul. This, too, has been rare. A 2017 New York Times Magazine investigation of nearly 150 U.S.-led coalition airstrikes targeting ISIS in Iraq found that 1 in 5 of the coalition strikes resulted in civilian death, a rate more than 31 times that acknowledged by the coalition. “Our reporting, moreover, revealed a consistent failure by the coalition to investigate claims properly or to keep records that make it possible to investigate the claims at all,” journalists Azmat Khan and Anand Gopal wrote.

The CIVIC-HRI team also noted that lessons learned from U.S. civilian casualty investigations are not systematically disseminated or implemented across the military, limiting the chances of avoiding similar incidents in future operations.

“While we found some examples of good practice in our review, these examples were overshadowed by the inconsistency — and, too often, inadequacy — of the overall record of military investigations,” said CIVIC’s Dan Mahanty, another report co-author. “From what we can tell, the military may even be shortchanging itself by not getting the total value out of its investigations.”