Private investigator, paranoid,fears his work will hurt someone, does not share personal info 70s 80s

Hello, i am looking for a movie i once watched on netflix.

The opening scene is of two people having a conversation in a public park/ space while the main character watches, and listens from a window using his “high-tech” equipment.

The main character doesn’t share any personal information with anyone including his girlfriend. No birthday, height, or address. He does this to hide his identity and to maintain integrity as an investigator.

The main plot follows his pursuit of a case however he fears the information he uncovers will get someone hurt. This has happened in the past so he vows to never let it happen again.

I remember other small details if those would be helpful I will post them in the comments.

Cheers!

The Conversation (1974)
starring Gene Hackman and directed by Francis Ford Coppola.
He is hired to eavesdrop on a conversation in a park with multiple microphones and high-tech equipment. Lives in a warehouse and is very protective of his methods/identity.