Details about why Iran air defense forces mistook a Ukrainian airliner for a cruise missile early Wednesday remain murky, but one thing is clear: Safeguards for operating surface-to-air missiles are supposed to prevent that kind of mistaken identity and all of them failed.

The error, which killed all 176 people aboard the plane, is probably the result of multiple layers of failure, said Steven Zaloga, senior analyst for missile systems at the Teal Group.

“There’s any number of potential problems here,” Zaloga said. “This incident strongly suggests that the methodology has failed and the technology has failed as well. There should have been a methodology worked out to prevent fratricide.”

Iran has vowed to conduct a thorough investigation of what happened, and bring the “culprits” to justice. Among the questions that remain is why authorities allowed civilian flights to operate during the tense hours after its attack on the Iraqi bases.

Ukrainian International Airlines Flight 752 was flying in a very different manner than the cruise missile it was supposedly mistaken for. It was following the normal departure path from Tehran’s airport and was clearly transmitting its identity when it was taken down.