That would be a matter of the sentence he received and the laws of the individual state. There are five general sentences that a convicted murderer may receive. Some a unique to particular states. These and the length of sentence are below:
There are some states that issue the sentence of life imprisonment. Also in these states, life may mean 20, 30, or 40 years. When the sentence is completed, the convicted person is discharged.
Usually, there is a term or length of time associated with this sentence. Where there is no length of time specified, it is likely the convicted person's file is reviewed periodically (annually, bi-annually, or every five years).
This is actual life imprisonment. There is no parole.
This is a more obsolete term, but some states may still use it. No parole.
Self-explanatory.