Very good considered responses from all sides here.
Look. Except for Jesus, Mary, and possibly John the Baptist and St. Joseph,
all people commit sins of varying seriousness.
In my 51 years, it has been my experience that most people lie and lie repeatedly.
Not necessarily MALICIOUSLY always, usually not with the intent to destroy an innocent person, but people lie quite a bit. And I have, too, and I am ashamed of it,
and am trying, not always successfully, to avoid doing it anymore.
We shouldn’t lie. It is sinful to lie. It is ESPECIALLY SINFUL to lie in order to do harm
to one’s neighbor, especially if he or she has done nothing wrong.
Is it always sinful to lie or remain silent in order even to protect yourself IF,
by coming forward and admitting your misdeed, you alone would not suffer, but innocent people could be ruined? I think in such a case, lying would be venial, but still regrettable. Remaining silent in such a situation would not be sinful at all.
Because deliberately putting innocent people at great risk of harm in order
to cleanse your own conscience, is a very selfish act. As long as you have a desire to atone for your misdeed and make reparation for it, you do not have to openly admit to it to others in order to be forgiven by God, especially if that would cause terrible consequences to innocent people. Of course, you do have to confess it to the Priest.
And remember, although all wrongdoing requires some form of intentional reparation for it, you do NOT have to personally hand a stolen item to the person you took it from. You can mail it to her or him, or have someone else give it back to them for you. If you are in no position to do that, do what you can: make a gift to the poor, or help bring people to Christ by donating to a rosary-distribution drive or something, and have masses said for the salvation of those you have sinned against and for the Holy Souls, in reparation.
Remember, even the Priest CANNOT, absolutely CANNOT, require that you go and accuse yourself to others, to ANYONE outside the confessional, not EVEN as a form of penance and he cannot require it for absolution, either. Now, if GOD REQUIRED that you publicly admit to your faults, that would not be the case.