嘘ついてたんだ vs 嘘ついたんだ


I saw this being said in a drama, when A said to B, 嘘ついてたんだ and the
translation was "So you lied!".

My question is, why is it 嘘ついてたんだ and not 嘘ついたんだ? Thanks.

Edit: How to tell the difference between the two?




When someone says 「[嘘]{うそ}ついたんだ。」, s/he is talking about the act which is
saying something untrue.

When someone says 「嘘つい **て** たんだ。」, s/he is talking about the acts which are
saying something untrue and keeping it secret for a period of time.

In many cases, 嘘つい **て** たんだ sounds more guilty than 嘘ついたんだ, although it
depends on the context.

