BERLIN (Reuters) - Police in the northern German city of Bremen said they had opened a murder investigation and were still seeking the suspected killer after a man who was shot in a supermarket on Thursday subsequently died of his wounds. In a statement, Bremen police said the killing of the 25-year-old man was not being treated as a terrorist incident and that they were still seeking the alleged killer, who appeared to have been known to his victim.  Initial indications are that the perpetrator and the victim knew each other,  they said.  The police have interviewed witnesses and continue to carry out urgent investigations.      