My blog post yesterday about re-ignited debate over the chemical attacks in Syria last August has brought a surprising response from some regular critics of the mainstream media.

On one side of the chemical weapons debate is Seymour Hersh, the veteran investigative journalist, who suggested in an article for the London Review of Books that rebel fighters, rather than the Syrian regime, were to blame for the Damascus attacks.

On the other side is Eliot Higgins, better known as Brown Moses, whose dissection/demolition of Hersh's article appeared on the Foreign Policy website.

Behind this dispute about who caused the sarin deaths there is also a conflict between two different approaches to investigative journalism and the sources that they use.

Unlike Hersh, Higgins is not a traditional journalist. He spends much of his time researching the Syrian conflict via the internet, blogging and tweeting about it.

Unlike Higgins, Hersh has little time for the internet, relying instead on mysterious but apparently well-placed sources to construct his case.

Following my blog post yesterday, Media Lens entered the fray on Twitter, siding with Hersh (here and here). Media Lens is a British website that specialises in critiquing the mainstream media, which it regards as "a propaganda system for the elite interests that dominate modern society".

Its position, if I've understood it correctly, is that journalists working in the mainstream media gradually acquire a "corporate" mindset which makes them less willing to challenge authority.

Given that Hersh has spent decades working for mainstream media, that Media Lens disapproves of anonymous sources, and that it encourages "the creation of non-corporate media", logic might suggest that it would have sided with Higgins. But no.

Although Hersh writes for the mainstream media he's also a dissenting voice within it. He exposed the Mai Lai massacre in Vietnam back in 1969 and, more recently, the horrors of Abu Ghraib prison in Iraq. Some of his other exposes have misfired, though, and he has often been criticised for his use of shadowy sources. In the words of one Pentagon spokesman, he has "a solid and well-earned reputation for making dramatic assertions based on thinly sourced, unverifiable anonymous sources".

Higgins, meanwhile, is the antithesis of a "corporate" journalist but the problem seems to be that he is not challenging western governments' views of the chemical attacks in Syria. His assessment of the evidence is that it points strongly to the Assad regime being responsible and, as far as some are concerned, that's enough to place him in the "corporate media" camp.

The real issue, though, is not Hersh versus Higgins or corporate versus non-corporate. It's about methodology. Hersh represents the old methodology – closed, elitist and opaque – while Higgins reflects the new – open, egalitarian and transparent.

A rather telling illustration of this is that while Higgins's Foreign Policy article invites comments from readers, Hersh's article for the LRB does not.

Higgins relies on open sources (mainly YouTube videos of the Syrian conflict) and draws conclusions from them. Anyone who disputes his interpretation is able to challenge it and, based on the ensuing arguments and available evidence, people can form their own view as to where the truth lies. It's a collective process that often takes twists and turns, but it's thoroughly transparent: the evidence is there for everyone to see and contribute to if they wish.

One example of how this operates in practice came when UN weapons inspectors determined the trajectory of two of the rockets implicated in the August attacks. Tracing their flight path on a map, Human Rights Watch found that they intersected in the compound of the Republican Guard's 104th Brigade.

That suggested the Republican Guard could be responsible if both rockets had been fired from the same position (though it's not clear that they were).

Further discussion on the internet established that the rockets had probably not come from the Republican Guard's compound because their range was too short. Some interpreted this as exonerating the regime, though subsequent video analysis by Higgins seems to show there were other places, within range, that the Syrian military could have used to fire them.

In contrast to that, the Hersh approach is a display of journalistic virtuosity. It relies on developing special contacts – seemingly well-placed figures who are willing to spill the beans, usually anonymously.

Anonymous sources can be valuable at times (without them the Watergate scandal would never have emerged) but they have to be treated with care and a lot hinges on the credibility of the journalist reporting them.

With anonymous sources it's hard for readers to know why they agreed to talk and whether they have any axes to grind or scores to settle. That's a judgment the reporter should make, though when presented with a juicy quote it can be tempting not to probe too deeply.

One of the key reasons for blaming the Syrian regime for the August attacks is that it is known to possess sarin and also the munitions that were used to deliver it, while the rebels are not known to possess either.

Hersh disputes this in his article, asserting that "the Syrian army is not the only party in the country’s civil war with access to sarin", and that "American intelligence agencies produced a series of highly classified reports ... citing evidence that the al-Nusra Front, a jihadi group affiliated with al-Qaida, had mastered the mechanics of creating sarin and was capable of manufacturing it in quantity".

"Citing evidence that ..." is a tricky phrase that doesn't actually tell us much. It may simply mean that somewhere in a plethora of intelligence material someone was quoted as saying that al-Nusra knew how to make sarin. The fact that claims to this effect may be been cited in intelligence reports does not necessarily mean they were assessed as credible.

Indeed, Hersh later quotes a named spokesman for the US Office of the Director of National Intelligence as saying that no American intelligence agency "assesses that the al-Nusra Front has succeeded in developing a capacity to manufacture sarin".

Hersh's source on the supposed sarin-manufacturing capabilities is an unnamed "senior intelligence consultant":

"Already by late May, the senior intelligence consultant told me, the CIA had briefed the Obama administration on al-Nusra and its work with sarin, and had sent alarming reports that another Sunni fundamentalist group active in Syria, al-Qaida in Iraq (AQI), also understood the science of producing sarin ...

"An intelligence document issued in mid-summer dealt extensively with Ziyaad Tariq Ahmed, a chemical weapons expert formerly of the Iraqi military, who was said to have moved into Syria and to be operating in Eastern Ghouta.

"The consultant told me that Tariq had been identified 'as an al-Nusra guy with a track record of making mustard gas in Iraq and someone who is implicated in making and using sarin'."

Manufacturing sarin is a difficult and dangerous business, as chemical weapons expert Dan Kaszeta has frequently pointed out. No one has yet come up with a sensible explanation, or even a plausible theory, as to how al-Nusra could have produced it in the quantities required for the August attacks. Undeterred by that, Hersh clearly wants readers to accept the word of his "senior intelligence consultant". But how are readers to judge? Presumably by being assured that the source is not just any intelligence consultant but a "senior" one.

Interestingly, though, EAWorldView has an idea who this consultant might be. It notes that Michael Maloof, who formerly worked in the US Defense Department, has made very similar claims in an article for the right-wing World Net Daily, and also on the Russian propaganda channel, RT.

If so, it's rather odd that Maloof is saying things to Hersh anonymously that he has already said publicly. Writing on the Air Force Amazons blog, Kellie Strøm comments:

"Given his association with what are widely regarded as crude propaganda outlets, if Mr Maloof is Mr Hersh’s anonymous source then his anonymity would seem designed more to protect Mr Hersh’s reputation than Mr Maloof’s."