was watching, was observing
Él sabe que alguien lo observaba.
He knows that someone was watching him.
— Moonrise Kingdom (2012)
Le observaba.
I was watching him.
Él comía y ella le observaba.
He ate and she watched him.
Él observaba la escena sin mucho interés.
He watched the scene without much interest.
Ella observaba cómo vuelan las mariposas.
She watched the butterflies fly.
Él observaba desde lejos.
He watched from afar.