Unfortunately, it appears that, despite the heavy level of sophistication, these devices were homemade with over-the-counter chemicals making them very difficult to trace.
14 seconds sound clip from the V for Vendetta movie soundboard.
You can hear this line at 00:12:19 in the Blu-ray version of the movie.
Quote context
[...]
- We also managed to get a picture of the girl that Creedy's men were detaining.
- Not sure yet, sir. But we're working on several leads.
- We located the fireworks launch and found traces of the explosives used at both sites.
- Whoever he is, chancellor, he's very good.
- Spare us your professional annotations. They are irrelevant.
- Gentlemen, this is a test. Moments such as these are matters of faith.
- To fail is to invite doubt into everything we believe, everything we have fought for.
[...]