insider
US /ɪnˈsaɪ.dɚ/
UK /ɪnˈsaɪ.dɚ/

1.
informante, persona de adentro
a person within a group or organization, especially someone who has special knowledge or access to information not available to outsiders
:
•
As an insider, she knew all the secrets of the company.
Como informante, conocía todos los secretos de la empresa.
•
The police suspect an insider helped the thieves.
La policía sospecha que un informante ayudó a los ladrones.