Updated

Formula One boss Bernie Ecclestone is back in a Munich court to answer charges of bribery in a case that could threaten his grip on the series.

Two German investigators were to testify on Friday on the second day of the trial of the 83-year-old, who appeared calm as he entered the courtroom with his attorneys.

The charges involve a $44 million payment to banker Gerhard Gribkowsky, who's serving an 8 1/2-year sentence for taking the money, allegedly to facilitate the sale of a Munich bank's stake in Formula One to a buyer of Ecclestone's liking.

When the trial opened last week, Ecclestone told the court in a statement read by his lawyers he was blackmailed into the payment by Gribkowsky.

Ecclestone faces up to 10 years in prison if convicted.