Hells Angels kept his mouth shut on the opening day of a trial in which he's charged with murdering a police officer "execution style."

Hells Angel biker gang member remained silent in a state courtroom in Koblenz on Tuesday, where the 44-year-old is charged with the murder of a police officer earlier this year.

The prosecution claims the Hells Angel shot the officer through the front door of his apartment in an "execution-style killing."

The officers had gone to search the man's apartment. The state prosecutor argued in court on Tuesday that the man " falsely recognized the officers as burglars" who had broken into his apartment before.

He fired two shots through the door at face-level in order "to punish" the burglars for the previous break-in, apparently not realizing that they were police officers.

The man said nothing when asked to explain the incident. It remains unclear how he will plead or whether he will even testify during the proceedings, which are to resume on October 1.

Dozens of police were present in and around the Koblenz court on Tuesday to provide security for the trial's opening.

At least five Hells Angels, a motorcycle gang widely recognized for crime and violent activity in Germany, were present in court for the opening proceedings.