It's a little bit more than media speculation however. The head of French counter-terrorism is a little more knowledgeable than the guy who cleans the office of the girl who knows a cousin of someone actually involved in the investigation I would think.
I might add that I'm writing this series in different parts so they will (potentially) add up to a cohesive whole. This particular "episode" focused on the explosives and in my humble and apparently underrated opinion, this issue is quite important.
If the explosives were "do it yourself" that a chemistry major could whip up in a bathtub with ordinary ingredients, that's quite frightening. It means that any terrorist, from the fanatical Muslim type to the Eric Rudolph Christian type to the Basque type to the white British neonazi type might soon be whipping up batches for more mayhem.
On the other hand, if these were military explosives, that's a major break. Because military explosives can be traced back to their origin, which might be an essential clue as to who orchestrated this event.
Pax Night and day you can find me Flogging the Simian
Ironically, the Scotsman sidebar leads to today's report that the investigators have still not identified the explosives used in the bombings. Likewise the FT cites unnamed intelligence sources - that appear to be just plain wrong about this.
The reality is, that poring over the contradictory press reports just illuminates how much noise there is propagated in the press, and how hard it is to discern the signal.
Why he would do so falls into the realm of the political... I'm curious however if "Balkans" is a codeword for "Czech Republic".
A lot of it was sold to Libya during the Communist era, when the Arab states were "friendlies".
Whilst he may have been in London assisting the investigation - he's not a ground-floor forensics investigator; and his language was hedged in such a way in the article for it to be clear that it was a speculative take.
There's also the prior event paradigm to take into account: seeing events in London in the light of events in Madrid, whilst "natural" - I certainly did to begin with - often leads down the wrong track. I doubt that Chaboud is any more immune to this than most of us - and I would certainly characterise him as someone likely to have a political agenda that he is seeking to advance.
I think that references to the Balkans would not include the Czech Republic. Specifically, I would guess that Chaboud is referring to the Former Yugoslavia or Albania, but I couldn't narrow it down any further than that. If he's referencing smuggled Balkan explosives then it's likely that he is making the obvious point that people and drug smuggling networks can also be used to smuggle explosives.
I think that one of the "issues" regarding this type of terrorism is that there is a DIY element to it - which makes it templateable and easily reproducible, elsewhere described as "open source" . This has obvious consequences when policy makers are always looking for state-based links and high-tech angles; AQ and affiliates are really "jiu-jitsu" practitioners, and are, as far as I can tell, interested in looking for low-tech, easily replicable methods.