LONDON, England – For investigators, it all started with a jihadi Web site that flashed the name of a group calling itself "al Qaeda in Britain."

From that new namesake there was, allegedly, a warning: Pull foreign troops out of Iraq and Afghanistan and release Muslims from a London high security prison or we will assassinate British Prime Minister Gordon Brown and his predecessor Tony Blair.

After months of investigation, four suspects have been arrested in England. They have not yet been charged.

At this point in proceedings, authorities are usually not very forthcoming on details, although police seem to maintain that so far they have no evidence that an actual plot was underway.

Was this a serious threat or was it an aspiration without any real consequence?

Trying to figure that out is always a dilemma for journalists. Do you give much voice to such a story – or are the threats so vacuous as to render them meaningless?

That's the problem for the media but it reflects a crucial and decisive investigative process for prosecutors.

Not only must security officials decide how serious any threat actually was, and possibly alter security arrangements, they also face a problem in deciding how to charge any possible suspects.

If the threats were credible, the charges could reflect the grave possibility of a political assassination in the making.

We keep asking ourselves "How big was this?" just as police keep asking for more time to question the suspects so they can try to figure that out.