"It wasn't Peter apparently." "It wasn't? Who could it have been?"
No era Pedro a lo visto.—¿No? ¿Quién estaría?
—TOMAYO Y BAUS.
Note that the conditional translates both could be and could have been.
116. To ring is tocar as a transitive and sonar as an intransitive verb.
We rang twice before we heard the bell ring within the house.
Tocamos dos veces antes de oír sonar la campanilla dentro de la casa.
At that moment a shot rang out very close.
En aquel mismo instante sonó un tiro muy próximo.
—ALARCÓN.