Always depends on the country and the way the convicts is acting in prison.
Some people might not want to believe it but in systems where convicts get support and where the goal is to reform them, murderers who are eligible for release (they are evaluated to be safe for society) have the lowest rate of recidivism of all criminals.
In Canada we are talking about 0.3% of all murder convicts that had previously been released after being convicted of the same crime or about one murder a year being perpetrated by a recidivist if you prefer.