Thank you, Kolo. The text clearly says the memorial service was for the terrorist victims around the world. It doesn't say Orthodox terrorist victims, and it makes no mention of the Trisagion Service, so maybe the OCA could explain this if someone wants to write to them.
In the Greek Orthodox Church I have never seen a priest, Archimandrite or otherwise, divest before performing a memorial Service after just finishing a Divine Liturgy. I do not know what the practice is in Slavic Churches.
I have never seen anyone devest before serving panikhida (parastas) memorial service immediately following the Divine Liturgy. There is no doubt that epitrachelion is required (just as with confession, or blessing of the home) as is the minimum amount of vestment required, not the maximum. In other words, I am pretty sure complete vestiture is not a problem, but less than epitrachelion is.
as is=and is