Behind bars means in prison. Put him behind bars, ten years behind bars, still behind bars.
It is journalists' language rather than legal language, and it is always about the fact of imprisonment rather than the sentence. Real cells often have doors rather than bars, but the phrase has outlived the design.
1phrasebehind barsIn prison.
“He spent four years behind bars before the conviction was overturned.”
behind bars is a phrase.
Practised in Idioms