The gang carried out 30 kidnappings, making millions of euros in ransom payments, the court heard.
In March 2005, the gang was destroyed when forces from the national security ministry freed the kidnapped wife of the country's largest bank, the International Bank of Azerbaijan, and arrested about 20 people. The captors had demanded a six million euro ransom.
Last year, while in prison waiting for the trial to begin, Haci Mammadov, the former criminal investigations chief, also confessed to the killing of Elmar Huseynov, a newspaper editor and prominent critic of the government.
He said that Farhad Aliyev, a former economic development minister, had ordered the murder.
Aliyev was sacked and arrested last year on charges of embezzlement and plotting a coup. He denies all the allegations.
Last year Azerbaijan was rated joint 130th in an index published by corruption watchdog Transparency International that ranked countries according to how corrupt they were perceived to be.