Nearly a week later, the atmosphere in the country has become poisoned by accusation and counter-accusation. Nobody has claimed responsibility for the bombing, the single worst incident in the three-year stand-off between Islamic fundamentalists and the military-backed government, uncomfortably reminiscent of the darkest days of Lebanon's civil war a decade ago.
Instead, conspiracy theories abound. Was a fundamentalist group responsible, as the government claims? Or could it have been the security services sabotaging one of their own strongholds in an attempt to discredit the fundamentalist Islamic Salvation Front (FIS)?
It is impossible to know for sure. There are no foreign observers or journalists in a position to conduct an objective investigation, and the local press has been muzzled by the authorities. The fundamentalist militias are heavily infiltrated by members of the security services, and vice versa. The extremists on each side grow more like each other every day, as voices of moderation are strangled into silence.
The bombing has brought an abrupt end to a month-long cycle all too familiar throughout the Algerian conflict: a cycle that always begins with high hopes of a breakthrough towards peace and always ends in hair-raising violence. Three weeks ago, opposition parties representing more than 80 per cent of the electorate signed a joint platform in Rome agreeing to a national conference that would pave the way to multi-party elections. The declaration, brokered by the Catholic Community of Sant'Egidio, did much to bridge the enmity between religious and lay parties and, most significantly, pushed the FIS for the first time into an unequivocal declaration of democratic values.
But the Algerian government refused to respond. Backed by a hard core of die-hard anti-fundamentalist "eradicateurs", it dismissed the declaration as the work of "retarded politicians" and organised a counter-demonstration in Algiers last Sunday. Diplomatic sources suggest the 10,000-strong crowd was moved more by coercion than enthusiasm, with soldiers seizing hundreds of identity documents and agreeing to return them only if people followed the march.
Even President Liamine Zeroual, who took office last April as a conciliator, moved unmistakably into the eradicateur camp as he stood by his unpopular programme for presidential elections by the end of the year.
The FIS soon dropped its conciliatory tone. Its armed wing threatened a bloody start to Ramadan, the holy month of fasting which began last Wednesday. Then on 27 January, three days before the Algiers bomb, one of the two FIS leaders under house arrest, Ali Belhadj, wrote a letter to the information minister warning that the crisis risked becoming deeper and more dangerous. "The next few days will show how," he wrote.
Suspicions that the FIS was responsible for the car bomb were only reinforced when its leadership took nearly three days to condemn it. One FIS source conceded that this was unusual, and that the attack had led to "intense discussion" on an appropriate response. Certainly, few fundamentalists seemed sorry to see police headquarters under attack. "Anyone who has been tortured in there would be tempted to offer up his life if he knew he could take the whole building with him," the source said.
On the other hand, the FIS certainly has more to gain in the short term by wooing moderates in the armed forces rather than taking them on. "Whatever the truth, the conflict is becoming more polarised," said Mario Marazziti of the Sant'Egidio community. "The prospect of dialogue is disappearing."
As if to reinforce this view, the Algerian government yesterday recalled its ambassador to France in response to the proposal President Francois Mitterrand made on Friday of a European Union peace initiative.