Walter Luebcke, who ran the Kassel area regional administration in central Germany, was found outside his home last Sunday by a relative. An autopsy confirmed a pistol shot to the head, fired at close range, and a homicide investigation was opened.
On Saturday, a man was taken into provisional custody in the case. Police said in a statement Sunday that he was questioned but let go in the early morning after "the questioning produced no indications that support a participation in the crime."
They said they would give no further information for now so as to protect the person and the ongoing investigation. Luebcke, a long-time member of Merkel's center-right Christian Democratic Union, in 2015 received threats after speaking out in support of helping asylum-seekers. The head of Hesse state's criminal police said last week that the threats from several years ago appeared to have no connection to the killing.
A funeral service for Luebcke is to be held in Kassel on Thursday, the local government told news agency dpa.