I believe theh must be aware of it in some form or another in order for them to gain black psyche-locks. Those people underwent events so traumatizing, they unsubconciously lock it deep inside their own hearts, effectively making it so that they're keeping secrets even from themselves.
There had only ever beem two such examples of black psyche-locks appearing. One, it was because the character in question was apparently so paranoid about whatever he's doing, he's keeping secrets even he's not aware of. The second was due to an incredibly traumatizing event.
Didn't Edgeworth also someone who went through a very traumatizing event (the DL-6 incident, where his father was shot and killed)?
So it's possible to break psyche-locks without even having a Magatama?