- The first sentence implies that something had happened to Angelita. I would suggest the following translation: "He pleaded his innocence from what happened to Angelita". The explanation that Nada has provided is also possible although less common.
- The second sentence means "He pleaded his innocence to Angelita / in front of Angelita".
It's always very helpful to provide more context to make sure we have the full picture before attempting to translate those sentences.