Thanks for that.
I, also, am still unclear as to how the one thing relates to the other. It seems reasonable to assume that the sentence has some relevance. I imagine that the author(s) put some thought into it. Perhaps not. I've not a lot of experience in such things to draw from.
Do you suppose it's an attempt to absolve themselves, soothe their consciences or pre-emptively rebut condemnation for their violence after some fashion?

Where's Tam?

Could simply be an Arabic idiom, like "don't say I didn't warn you".

It would be more interesting (and potentially more relevant) if this passage was cited in fundamentalist literature. Qutb or somesuch, as a justification for killing innocents. That sort of thing is not easily found online.

However, the Qur'an does issue fairly strong condemnation against killing without justification:

...That if any one slew
A person - unless it be
For murder or for spreading
Mischief in the land -
It would be as if
He slew the whole people:
And if any one saved a life,
It would be as if he saved
The life of the whole people. (5:32)

Seen from this perspective, it makes sense that Islamist terrorists might want to "justify" their behavior to non-extremist Muslim readers, or create the impression that this is somehow justice in accordance with Islamic principles.

As with other fundamentalist/literalist groups, it's pretty common to condemn every religion (including sects within the same faith) as "false". Shi'a Muslims were historically harassed/persecuted for not adhering to mainline (Sunni) beliefs and modern fundamentalists likely hold the view that Shi'a practices/beliefs put them outside normative Islam, along with other Unbelievers. Perhaps Sunni fundamentalist teachings include this bit of history as a parable for action against those who would endanger the faith, excusing extreme and horrific violence by issuing a warning beforehand.

Re: Tam, hoping he'll show up and offer some insight. This is not my area of expertise, really :)

It may reveal some Qurannic reference, but I doubt it's anything more significant than a convenient expression to put justice on their side. After all, most extreme wahabist or fundamentalist practices are justified by some interpretation of the Quran. Showing the links to the Quran isn't going to help us understand them better in terms of what they'll do, since they'll simply act as they please and use the Quran to justify themselves afterwards. It might provide other insights.

It may also be on some level an encouragement to the fledgling Al-Qaeda wannabes to only act on warnings given by Bin Laden or some other "authority" in the "organization". In that way, policy can be enacted by simply issuing threats, and watching the sub groups act on those threats. Of course its just as likely these groups receive direct support anyways.

Unless it is a particular reference to a well-known or studied story or text, it seems simply a standard way to justify mass murder to the less convinced. "Well, we warned them." (Even if the warning is vague and general.)

Defenses, for example, of the Irgun's bombing of the King David Hotel sometimes make a big deal of the alleged pre-warnings given. I can think of some pro-IRA literature which make a point to quote a government cop as saying it was "damned decent" of the IRA to warn him he was a target.

http://www.daat.ac.il/daat/english/history/lapidot/17.htm

"After exiting the hotel, Gidon summoned two Irgun girls who were waiting nearby, and ordered them to carry out their mission. They ran over to a nearby telephone booth, and delivered the following message to the hotel telephone operator and to the editorial office of the Palestine Post:

'I am speaking on behalf of the Hebrew underground. We have placed an explosive device in the hotel. Evacuate it at once - you have been warned.'

They also delivered a telephone warning to the French Consulate. . . The telephone messages were intended to prevent casualties. "

Sorry folks, but I've not much to add. Far as I can determine they are saying that there hands are clean of blood because they have warned said governments of the consequences of their acts and been ignored.

Ubayd Allah b. Ziyad had warned the community not to cause dissension, but Husayn had risen in rebellion anyway. Ubayd's hands were therefore clean in his massacre at Karbala.

Of course it is rather curious that Islamists would seize upon this little speech ( if they did ), because I believe even most Sunni traditions tend to regard Karbala as a tragedy and Ubayd ibn Ziyad comes off pretty bad in just about every account ( of course Abbasid hagiographers weren't always too kind to the actions of their Umayyad predecessors, Umar II excepted ).

An interesting comparison, eerie. May I inquire as to how you acquired knowledge about this apparently monumental event. By the way, what I've gathered, embarrassing eavesdropping included, is the fact that this incident and the Shi'ites are generally not favourable topics for discussion here in the MENA region with the overwhelming majority of the populace. A quick search on various encyclopediae and from conversation with certain peers of mine belonging to the sect reveals the fact that the Ummayyad dynasty, along with the Abbasid dynasty were the proponents, as it were, of the use of "legitimised" violence in order to subdue followers of other sects, assigned the moniker "unbelievers" and considered to be "outside the pale of Islam". Once again, that's an interesting parallel you've managed to draw up with the London bombings, which by all accounts, are an unpardonable, similar about to the Karbala incident. Keep up the good work.

Tam - Well, fundamentalist Sunnis have a notoriously narrow view of what constitutes "Islam", so it wouldn't surprise me if the Shi'a were painted with the same brush as non-Muslims by extremists. Not specifically because of Husayn/Karbala, but because of the doctrinal differences and misunderstandings that emerged later on.

It just seems to me that fundamentalists might be more familiar with early Islam and events like Karbala, seeing as so much of the theology/philosophy that comes later is rejected by them. Not an attempt to rationalize "he who warns is excused" but I'm curious about the ideas/interpretations extremists adopt to justify these acts to themselves. Especially in light of ayat like the one I cited above - strictly speaking, warnings do not absolve.

AED - Thanks for the kind words. My knowledge is generally a mix of formal/informal learning and observation.

Re: legitimized violence against "minority" sects, it's certainly a common theme in early Islamic history (that is until the large Sunni dynasties gave way to smaller, often Shi'a-backed rulers).

Takfiris (the hardliners of the fundamentalist Salafi movement) generally regard Shi'ites as apostates who worship the dead and therefore completely fair game - which for them legitimises the violence against the Shi'a in Iraq at the moment. Karbala for them is the epitome of fitna which means damaging dissent/strife amongst the Umma.

To justify the bombings with a reference to the prelude to the Karbala massacre sounds about right, to me - they get to make two points in the same quote: a)we warned you, and b)we're the intellectual heirs of the pious companions of Mohammed.