One of Sweden's best known business leaders, Rollen has always denied any wrongdoing and continued to run Hexagon, which he has led since 2000, transforming it from a lowly-valued conglomerate into a $20 billion technology market leader.
Rollen, who was cleared of all accusations in an unanimous verdict last year, risks a prison sentence if found guilty over his October 2015 purchase of shares in Next Biometrics, a Norwegian firm unconnected to Hexagon.
The case concerns Rollen's purchase of Next shares on behalf of Greenbridge, an investment firm he co-founded. Prosecutors said this was illegal because Greenbridge was involved in talks to take a larger stake in Next at a higher price.
"What is the key in this case? Rollen bought shares at the same time that he had insider information," lead prosecutor Marianne Bender told the Borgarting appeals court. "He cheated. He knew something that other investors did not know."
Asked by judge Eirik Vikanes if he admitted any guilt, Rollen replied "No".
During his trial, Rollen's defence team argued successfully that the Next trades did not violate the law.
"Ola Rollen must be acquitted. He has not committed insider trading," his lawyer Christian Hjort told the appeal hearing, which is scheduled to last until May 29.
Bender, the prosecutor, has argued that the district court's interpretation of insider trading rules was flawed and that the original verdict also gave a wrong evaluation of the evidence.
At the first trial, prosecutors had asked for an 18-month prison term, out of a maximum penalty of six years. They have not said whether they will seek a similar sentence this time.
While Hexagon's shares fell by 10 percent in 2016 on the news that Rollen had been detained by police, they have risen by 24 percent since his acquittal in January 2018.
On Wednesday, shares in the company were up 1.0 percent to 527.6 Swedish crowns at 0832 GMT.
(Reporting by Gwladys Fouche, writing by Terje Solsvik, editing by Alexander Smith)
By Gwladys Fouche
