Restorative justice is used for serious crimes including murder (it is especially effective for this level of serious felonies), but usually it’s only used after a person has pleaded guilt. Last year the Oprah Winfrey Network did documentaries of 4 cases concerning homicides that were held in prisons (I facilitated one).
Face-to-face restorative justice meetings are almost always used after conviction or for diverting cases before they go to the criminal justice system or trial for resolution. I've never heard of a murder case being diverted, neither had Tullis who wrote, “no one I spoke to had ever heard of restorative justice applied for anything as serious as murder” for diversion. Yet, it would be possible to divert a murder case to a restorative process, and maybe any that have been diverted have not been discussed because of the potential for political backlash (e.g. alleged failure to be “tough on crime.”)