Two other professional musicians , violinist Jean le Boulaire and cellist Étienne Pasquier , were among his fellow prisoners , and after he managed to obtain some paper and a small pencil from a sympathetic guard , Messiaen wrote a short trio for them ; this piece developed into the Quatuor for the same trio with himself at the piano .
Two other professional musicians were also among the prisoners : Jean le Boulaire , a violinist and Étienne Pasquier , a cellist .