If the
third people are the subject of the action the relative pronoun 'whom' is used:
The girl with whom I spoke was from Argentina – La muchacha
con quien hablé era de Argentina
The man to whom I gave the key was the owner – El hombre a
quien le di la llave era el dueño
The writer
from whom I received this script is well known – El escritor de quien recibí
este guión es bien conocido.