telling a lie is saying something that isn't true. Not telling the whole story is just leaving parts out, but everything that does come out of your mouth is true. It isn't necessarily honest, but it is true
Question: "Do you know who killed this guy?"
Answer: "I do know who killed that guy. *doesn't say who killed him*"
I left out half the story. Not a a lie.
Well in a court of law, when testifying under oath, you are to tell the truth, the whole truth and nothing but the truth. Lying under oath or perjury is committed when you either say something that isn't true or leave out parts of the truth.
Answer: "I didn't (see the woman with the gun) kill that guy" ?
That's a lie.
Answer: "I do know who killed that guy. *doesn't say who killed him*"
I left out half the story. Not a a lie.