clay bird,
Annex 13 specifies the protocols on accident investigation, until we have an accident we don't have an accident investigation, do we? We have a missing/overdue aircraft right now. If the wreckage is found, the state of occurrence (where the wreckage is located) will be in the investigatory body. If in international waters, it will be the state of registry (Malaysia). The only legal position for the US, thru the NTSB, is to be invited to the investigation as an accredited member. Right now, the US's role is as one of the few nations with the resources, skills and knowledge to assist the Malasians, as such, we have no legal means to "takeover".
GF