Jihad Watch provides more clues pertaining to the Armanious family murders: http://www.jihadwatch.org/archives/004740.php

“The Armanious family had inspired several Muslims to convert to Christianity — or thought they had. These converts were actually practicing taqiyya, or religious deception, pretending to be friends of these Christians in order to strengthen themselves against them, as in Qur’an 3:28: ‘Let believers not make friends with infidels in preference to the faithful — he that does this has nothing to hope for from Allah — except in self-defense.’
Of course, the family, not suspecting the deception, was happy to see the ‘converted’ men and willingly let them in to their home. That’s why there was no sign of forced entry. Then the ‘converted’ Muslims did their grisly work.

Many Copts are regarding the murders as a warning to the Coptic community as a whole, related to the increasing strife between Copts and Muslims in Egypt and the Copts’ energetic efforts in America to get the truth out about the differences between Middle Eastern Christians and Muslims — differences that the Islamic lobby, with its disingenuous talk of ‘Arab Americans,’ routinely glosses over and hopes you don’t notice. The Copts, to their immense credit, have been particularly outspoken among Middle Eastern Christians about Muslim oppression. And yes, many are active on Pal Talk debating Muslims.

The nature of the warning? The murders send a signal from the Muslims to the Copts: we are going to behave here the same way we behaved in Egypt, and the First Amendment and American law enforcement will not protect you. Don’t expect America to keep you safe from us. The oppression and harassment you thought you had left behind in Egypt has now come to you …”