Bernie Ecclestone's blackmail defence came under attack on Friday, as the F1 chief executive returned to court in Munich.
Ecclestone has claimed he made the disputed $44 million payment to Gerhard Gribkoswky only because the jailed F1 banker was threatening to release information to the British tax authorities.
Prosecutors, however, allege 83-year-old Ecclestone bribed Gribkowsky in order to influence the sale of the sport's commercial rights and remain in charge.
On the witness stand on Friday was an investigator who interviewed Ecclestone during the Gribkowsky affair three years ago.
Public prosecutor Martin Bauer suggested Ecclestone's explanation of blackmail lacked detail.
"It was never really clear what form this threat (from Gribkowsky) could have taken," he is quoted by the Telegraph newspaper.
"(It was) like a vanilla pudding that you can't nail to the wall," he added.