During his time in prison, he tested positive for drugs three times, with the last incident happening in 2011.
A psychologist report recommended that Namana complete the Special Treatment Unit Rehabilitation programme, an intensive nine to 12 month programme for serious offenders.
Namana had been housed in the internal self care unit, where he had been helping to train disability dogs.
However, the board found that Namana still had further work to do in addressing his violent offending.
"He clearly has considerable work to get on with to mitigate his assessed high risk of violent re-offending and moderate risk of general recidivism.
"He also needs to formulate a robust safety and release plan and demonstrate, over time and in a variety of situations, that he can put into practice the lessons learned in the programmes.
"Until he does so he will continue to pose an undue risk to the safety of the community."
Parole was denied.