Am I the only one who finds this to be highly irregular? Until the exact cause of this accident is known, is it proper to have engineers from the manufacturer, an obvious interested party in the outcome, advising on the (mis)handling of the evidence?
Civil accident investigations in most (but not all) ICAO countries are based on mutual cooperation from all the interested parties. That's because the intent is not to assign "blame" or "liability" but to find the root cause of the accident so we can improve aviation safety for all.
Airbus (and Boeing) would rather find something wrong and definitely fix it, than having rumours that they covered up a flaw and that their planes are suspected to be unsafe. If the public cannot have confidence in the manufacturer, that's the quickest way for them to lose customers. Besides, even if Airbus were to be found to be at fault, they have insurance to cover any liabilities.
A safety investigation is very different than criminal proceedings in many countries. In Indonesia (similar to the US), any wreckage / evidence sensitive to investigations will be under control of the country's transportation safety board -- unless and until a criminal element is found.
In other countries (such as Italy, Japan), accidents are treated as criminal cases first, and will be under the jurisdiction of police with very strict custody handling / chain of evidence procedures, until criminal action can be definitively ruled out.
In some cases, this "interference" from police and the adversarial nature of criminal investigations have delayed and compromised safety investigations.