In the weeks before the New Year's Day suicide bombing of an Egyptian church, al-Qaeda-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 Islamic hard-liners have been holding weekly anti-Christian demonstrations.

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 that they were inspired by al Qaeda.

Before the attack, al Qaeda 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 posting includes the "Jihadi Encyclopedia for the Destruction of the Cross," with 10 videos describing how to build a bomb.

In the videos, an unidentified militant in a white lab coat and a black mask lists the ingredients for TNT and mixes them in beakers.

The site lists Coptic Christian churches in Egypt, along with phone numbers and addresses -- including Saints Church.

Security officials say they were aware of the online manual before the bombing and are examining any links between it and the material posted on Islamic websites.