In the weeks before the New Year's Day suicide bombing of an Egyptian church, al-Qaida-linked websites carried a how-to manual on "destroying the cross," complete with videos on how to build a bomb and the locations of churches to target — including the one that was attacked.
They may have found a receptive audience in Alexandria, where increasingly radicalized Islamic hard-liners have been holding weekly anti-Christian demonstrations, filled with venomous slogans against the minority community.
The blast, which struck Saturday as worshippers were leaving midnight Mass at the Mediterranean city's Saints Church, killed 21 people.
President Hosni Mubarak has accused foreign groups of being behind the attack, which has sparked a wave of angry protests by Christians in Egypt.
But on the ground, investigators are searching in a different direction — scrutinizing homegrown hard-liners, known as Salafis, and the possibility they were inspired by al-Qaida.
Only two or three days before Saturday's bombing, police arrested several Salafis spreading fliers in Alexandria calling for violence against Christians, a security official said. He spoke on condition of anonymity because he was not authorized to talk to the media.
According to authorities, the strong belief among investigators is that local extremists who knew the area and the nature of their target were behind the blast. The Egyptian weekly Al-Youm Al-Saba said police were examining photos of the Salafis' weekly protests for suspects.
In the weeks before the attack, al-Qaida militants on the Web spewing calls for "jihad," or holy war, on Egypt's Christians laid out everything anyone would need to carry out a bombing.
One widely circulated posting includes a so-called "Jihadi Encyclopedia for the Destruction of the Cross," with a series of 10 videos describing how to build a bomb.
In the videos, an unidentified militant in a white lab coat and a black mask is shown listing the ingredients to make TNT and mixing up the chemicals in beakers.
The site lists Coptic Christian churches in Egypt, along with phone numbers and addresses — including Alexandria's Saints Church. "Blow up the churches while they are celebrating Christmas or any other time when the churches are packed," it says.
Security officials say they were aware of the online "how-to manual" before the church bombing and are examining any links between it and the material posted on Islamic websites.
One main Salafi group, the Salafi Movement in Alexandria, issued a statement condemning the bombing, saying its preachings "reject such practices."
The ultra-conservative Salafi ideology has been gaining followers throughout Egypt in recent years, preaching a return to the ways of early Muslims. It calls for strict segregation of the sexes and rejection of any religious "innovations," such as permitting boys and girls to attend school together or collecting interest on bank loans.
The movement has spread across class lines, among wealthy businessmen, the middle class and urban poor. Men grow long beards and shave off mustaches, to imitate the Prophet Muhammad. Women wear the black niqab robes and veil, which envelop the entire body and face, showing only the eyes.
In many ways, it resembles the doctrine of al-Qaida, with one major difference — while it advocates jihad against "foreign occupiers" in Iraq or Afghanistan, it rejects holy war inside Egypt, at least for now.
But many observers warn that some members are growing more radicalized and have begun to advocate jihad within the country, providing fertile ground for al-Qaida influence.
They cite the group's unprecedentedly fierce campaign against Egypt's Coptic Christian Church.
It was sparked by the case of two Christian women who reportedly converted to Islam to get divorces from their husbands, since the church bans divorce. The Salafis accuse church officials of forcing the women to renounce Islam and return to Christianity, a claim the church denies.
At weekly protests attended by hundreds outside mosques in Alexandria and Cairo, Salafis have accused the church of holding the women against their will. Vowing vengeance and denouncing Coptic Pope Shenouda III as an "infidel," the protesters accused Copts of trying to "Christianize" Egypt's Muslims and stockpiling weapons in churches and monasteries.
In September, one Salafi cleric, Ahmed Farid, wept as he told worshippers at an Alexandria mosque that Muslims were being "humiliated" by Christians, chiding them for "giving up jihad."
At a Salafi protest in Cairo in October, some raised the flag of al-Qaida in Iraq — a black banner emblazoned with the phrase "there is no god but God and Muhammad is God's prophet."
Two days later, al-Qaida in Iraq attacked a church in Baghdad in a siege that left 68 Christians dead, the worst attack ever against Iraq's Christian minority. The group issued a statement vowing a campaign against Christians unless the two women in Egypt were freed, and several other attacks on the community in Baghdad have followed.
Since then, calls on al-Qaida-linked websites for attacks on Egypt's Christians have grown to a fever pitch.
A statement posted with the videos decries the failure of Muslims to act to free the two women.
"Will we keep on dreaming and dreaming, or is it time to wake up to the echoing boom and the flying torn limbs that will please the faithful and scare the infidels?" the statement reads. "Of course, it is better to act as a group, but that must not be an impediment between you and action. ... Move forward on your own."
The threats raise the question of why security officials did not do more to protect churches. On New Year's, Saints Church had only three or four policemen outside and cars had easy access to the street.
Copts, who make up about 10 percent of Egypt's nearly 80 million people, accuse the government of ignoring threats against them and doing nothing about growing anti-Christian sentiment.
Experts say the government has tacitly allowed the growth of Salafism because it is not anti-government and does not get involved in Egypt's politics, as opposed to the fundamentalist Muslim Brotherhood, which is the regime's main political rival.
"The Egyptian regime is harvesting the sour fruits for letting this extremist thought to grow and recruit thousands of young Egyptians," said Rifaat Sayyed Ahmed, an expert on Islamic groups.