Did the Tsarnaev brothers act alone or were they part of a wider conspiracy?

That is the pressing question facing investigators in the wake of the Boston bombing. Given that one of the terrorists is now in custody it's likely some kind of answer will now be forthcoming. But in making their assessment, investigators, besides using interrogation, will look to clues in the terrorists' "technical education" and "tradecraft" – the bomb-making, targeting and deployment processes.

There are thousands of how-to websites on topics from improvising explosives and timing devices to formulating biological toxins such as ricin. In the aftermath of last week's attack, analysts flagged up certain "technical" factors as significant. There was the fact the bombs were small, "homemade" pressure-cooker devices filled with a low-velocity improvised explosive mixture and packed with nails or other improvised shrapnel. Though dangerous enough to kill, these were far from sophisticated devices.

Technical considerations aside, the terrorists clearly "amateurish" tradecraft equally points to them being what intelligence analysts call "grassroots militants" or "lone wolf" actors. In security service parlance, tradecraft refers to the skills needed by both terrorists and intelligence officers to conduct clandestine activities in a hostile environment without discovery.

Unlike the technical skills of rudimentary bombmaking that can be taught in a makeshift classroom or gleaned from the internet, tradecraft often requires subtle and complex skills that frequently run counter to human nature and are difficult to master. Getting caught on CCTV was the first sign of the Tsarnaev brothers' obvious tradecraft incompetence.

Tamerlan Tsarnaev, the older of the two terrorist brothers also linked his YouTube page to a video entitled "The Emergence of Prophecy: The Black Flags From Khorasan". The video, translated by the independent SITE Intelligence Group that monitors jihadist and other terrorist groups, was reported as far back as October 2011 after being posted online by a terror group from the Afghan-Pakistan region. The video was a rallying call for jihadists in the Caucasus region and beyond. The fact Tamerlan openly linked to it suggests he was less than scrupulous when it came to covering his online tracks with effective tradecraft.

Even Dzhokhar, the younger brother now in custody, is said to have tweeted in Russian on April 21, 2012, almost exactly a year ago to the day of this capture: "I will perish young." Last August, he also posted on Facebook that the "Boston marathon isn't a good place to smoke tho'."

None of this seems to have been picked up by US security services despite reports the elder Tamerlan had been under surveillance for three years or more and the FBI had checked his online activity. If true, effective tradecraft it seems was also lacking with the US authorities.

The Tsarnaev brothers' actions seem consistent with a trend of jihadists shifting to lone wolf-type behaviour in contrast to the more centralised militancy seen in the years before 9/11. No group has exemplified this shift more than al-Qaeda, which has devolved from a distinct organisation with a clear political aim to a franchise, or looser network, supporting al-Qaeda's cause.

Dzhokhar Tsarnaev now lies in a serious condition in hospital. With him, too, lie definitive answers to the questions around a shocking terrorist conspiracy.