It's possible you're thinking of another character or you've misremembered something. Could you clarify who you're referring to?
Perhaps you're thinking of:
* Toby Cavanaugh: Toby was initially believed to be "A" but was revealed to be a victim of "A" just like the girls. He knew some secrets because he was dating Spencer Hastings and was involved in the investigation.
* Ezra Fitz: Ezra was initially a teacher who was dating Aria Montgomery. He was revealed to be "A" in the series but only knew some of the girls' secrets due to his past connection with Alison DiLaurentis.
* "A" team: The identity of "A" changed throughout the series. Each person who was "A" had access to the girls' secrets through various means, like hacking, surveillance, and blackmail.
To help me answer your question accurately, please provide more context or details about the character you're referring to.