You learned the に reading for this kanji when you learned 逃げる.
If you have trouble telling the two words apart, remember that if you're going to let go of someone, make sure they have their knee guards (にが). It's a dangerous world, you can't have them running free without some extra protection, you know.
We can’t let the criminal escape.
I've infiltrated this facility to set free the hostages who are being held here.
He was a real stitting duck, but we let him go.