"Private criticism" is a favourite tool of the Guardian's political reporters. It means that someone can have a free hit at their opponent without comeback.
There has also been private criticism of the way the IPCC has conducted its first high-profile investigation since the watchdog body was reformed and made independent of the police.
"This was London in the grips of an attack, two weeks after another terrorist attack had killed 52 people," said one source. "Four men were on the run who could have attacked again, the events of the day were extremely fast moving. There is a sense that the IPCC, having failed to recommend any action against any of the officers involved in the shooting itself needed a scapegoat."
And the Guardian tells us:
in the immediate aftermath of the shooting, sources say there were unconfirmed rumours that the man who had been killed may not have been one of the four suicide bombers being hunted. Mr Hayman is criticised by the IPCC for not passing this on to Mr Blair at a briefing he had with him at 6pm that night.We'll have to wait and see whether "unconfirmed rumours" and "unsubstantiated rumours" are valid descriptions of the information that the police had at that point. In the first place, there was never a positive identification of De Menezes as one of the suspects so the starting point was that he "may not have been one of the four suicide bombers being hunted". But surely the police had solid ID evidence almost immediately.
However, senior sources question how he could have passed on the unsubstantiated rumours at that stage.
Or perhaps the police were more incompetent than we thought. Perhaps with four men on the run who could have attacked again they failed to check that the one they thought they had accounted for was actually one of them.