This might be entirely coincidental, but regardless, I can see why observers would find it not adequate.

However, more crucial here is that AI does not have any official monitoring status. Sure, they have good reputation, but ultimately are "just" an NGO. It might have been a different story if this was an official (UN) body safeguarding fair trials. But I'm not even sure if those exist, given that courts are often considered an "internal affair" of a country. If there's something wrong with them, the official way is usually to proceed to an international court, after having exhausted your options in a national court.

Also, AI itself is not without controversy. It certainly does a lot of good work, with most people involved having nothing but good intentions. That said, I have personally witnessed how the organization (at least once) made some seriously politically damaging statements for a ruling government, but as it later turned out based on false information. That itself can happen. But when AI was privately informed (with evidence countering their statements), about how they were used for a political agenda, they still held on to their initial stance. That was rather surprising and even shocking to me, for an organization like AI. Only years later, did I finally hear about questionable personal relationships between the local political opposition and AI staff. From what I've heard since, that was neither the first time that AI wasn't as politically (or nationally) neutral as often thought/claimed.

I doubt that the above has much relevance in this particular case though. Still, apparently AI isn't always above using information "tactically" for their own and/or political means/ends.