Which is to say that they are following the same line as General Peter Pace: We don't know if the Iranian government is responsible, or "rogue elements." A good way out if you don't want to fight back. And nice ammunition for the peaceniks.
That is in part to ask, are Iranian military elements with access and wherewithal to carry out the missile shoot-down of a low-flying, five-person British Wing Commander's helicopter over Basrah likely to be "rogue" or likely "undocumented foreign fighters?"
(Can one find truly "rogue element" activity from the US military since "Kelly's Heroes," outside the CIA?)
HF