By Jim Muir
BBC News, Baghdad
Many Iraqis were not surprised at the existence of the interior ministry centre where detainees were allegedly tortured, abused and starved.
They were surprised that its existence has been revealed, creating a local and international scandal.
Sunni groups alleged that Iraqi police have been involved in torture
For months, international human rights groups and Iraqi political factions - especially Sunnis - have been complaining about irregularities and abuses.
Many of the accusations have been levelled at units operating in the shadow of the interior ministry.
Sunni groups such as the Iraqi Islamic Party (IIP) have frequently accused Shia militia elements of taking over parts of the ministry apparatus and operating death squads with a sectarian agenda.
"The IIP has announced over and over again in its communiques that there are elements wearing interior ministry uniforms raiding peaceful houses under curfew at night and detaining dozens of innocent citizens," said a statement issued by the IIP.
"A few days later their bodies are found, sometimes thrown in the Badra and Jassan areas, sometimes in the Tigris river, and sometimes in Nahrawan and elsewhere."
"Every time we've raised the issue with the US forces or the Iraqi government and asked them to investigate and stop these massacres and set things right, all we received was denial and silence," the statement concluded.
When the current transitional government was formed in April, the interior ministry was given to Bayan Jabr al-Zubeidi, a commander of the Badr Brigade.
The brigade is the military wing of the Supreme Council for the Islamic Revolution in Iraq, one of the biggest religious factions in the Shia coalition that dominates the transitional government.
It was not long before complaints began to circulate that large elements of the Badr Brigade were simply being incorporated into the ministry, whose special units - with names like the Wolf Brigade and Scorpion - became feared in the Sunni areas where the insurgency is rooted.
A government-linked Shia militia has denied involvement in abuse
On the streets of Baghdad, many police vehicles still carry the Badr Brigade's green ribbon in addition to the official red and blue police insignia.
For its part, the Badr Brigade has denied any wrongdoing.
"This bunker is run by the interior ministry, the Americans are there every day," Badr head Hadi al-Amery told Reuters.
"Badr has nothing to do with this, why would Badr be involved in the first place? If there was torture we ask for an investigation."
The Americans must clearly have been aware of the overall situation at the interior ministry as well as of the specific accusations being made.
Was their dramatic move on Sunday night, surrounding a ministry building, driving its guards out and taking it over, conducted simply in pursuit of a missing teenager, as they asserted?
Or was there a political angle to the development and its timing?
Discrediting Iranian-backed religious Shia factions in advance of the December elections is clearly not something that would cause officials in Washington to lose sleep.
US officials are also eager to persuade Sunni leaders and factions to participate fully in the elections and the subsequent government, and to encourage their communities to vote.
Abuses carried out under an official cloak are not something that can be publicly defended once exposed
Winning hearts and minds among the Sunnis is seen as essential if the Sunni-based insurgency is to be defused and its hard core of inveterate Baathists and Islamic militants isolated.
That task is clearly an uphill one as long as the Sunni perception remains that the US-backed government, dominated by a coalition of Shias and Kurds, is being used as cover for sectarian reprisals against the Sunnis.
If that is indeed what has been happening, there are plenty of reasons why angry Shias would want to wreak revenge against the Sunnis.
They suffered heavily under the Sunni-based regime of Saddam Hussein.
The Sunni insurgency has also perpetrated numerous highly-provocative outrages against Shia civilians and holy sites, killing many hundreds of civilians.
Human rights groups have made repeated accusations of abuse
But abuses carried out under an official cloak are not something that can be publicly defended once exposed.
The revelations will inevitably further discredit a Shia-dominated government that has won few plaudits for its performance.
The highest eminence in the Iraqi Shia religious firmament, Ayatollah Ali Sistani, had already decided to withhold his blessing from the Shia coalition that is contesting the December elections, because of his reservations about the government's performance.
The revelations can be expected to make it even more unlikely that he will change his mind with the approach of the 15 December polls.
In the January transitional election, the ayatollah's implicit backing for the Shia coalition was believed to be a major factor persuading the Shia masses to vote for it.