The EU court imposed strict measures to protect the prosecution witness in the so-called Medicus case, named after the Medicus clinic where the alleged crimes took place.
The second day of the trial was closed to the public and the media, with even some 20 relatives of the seven suspects, who gathered at the court entrance heavily guarded by police, refused entry.
According to court sources the witness is one of the victims of organ trafficking, who now only has one kidney. "The Medicus case is one of the most important cases that the (European Union rule of law mission) EULEX has dealt with," the EU-mission's spokesman Blerim Krasniqi told AFP.
They defendants face charges of "human trafficking, organised crime, unlawful exercise of medical activity, and abuse of official position or authority," he added.
The seven suspects, six of whom are doctors, went on trial on Tuesday before a panel of judges composed of two European magistrates and one local judge. All seven have pleaded not guilty. They are accused of organ trafficking and illegal organ transplants at a private Pristina hospital.
According to the indictment, victims were recruited from poor Eastern European and Central Asian countries. They were promised about 15,000 euros ($19,440) for their organs, while recipients would pay up to 100,000 euros each.
The most prominent defendants, who according to the indictment formed "an organised criminal group”, are former health secretary Ilir Rrecaj, and Lutfi Dervishi, a prominent urologist.
Rrecaj is accused of having issued a licence for the Medicus clinic even though Kosovo law forbids organ transplants. Dervishi is alleged to have set up the whole organ transplant network.
Other suspects in the Medicus case also include Turkish doctor Yusuf Sonmez, said to have performed organ removal surgeries and Moshe Harel, an Israeli accused of having matched donors with recipients.
Last month in Istanbul, Turkish public prosecutor indicted Sonmez and Harel over the case and requested a 171-year prison sentence for each.
The Medicus clinic was raided and closed by police in 2008 after a probe was launched when a young Turkish man collapsed at the Pristina airport after donating a kidney to an Israeli man.
This trial is not directly related to allegations of organ trafficking made in a Council of Europe report against Kosovo Prime Minister Hashim Thaci and other senior commanders of the ethnic Albanian guerrillas during and after the 1998-1999 war with Serbia.
But EULEX has also opened a probe into that report and recently appointed US prosecutor John Clint Williamson to run the investigation.
Local observers noted EULEX's persistency in getting to the heart of the Medicus case. "So far EULEX has demonstrated it's extremely serious in treating all the details of the case," journalist and legal specialist Vehbi Kajtazi, told AFP.
"This case is considered as the one of the biggest cases linked to international illegal trafficking in which Kosovo is involved," he added. The 3,000-member EULEX mission was launched as the biggest European civil operation ever just months after Kosovo declared independence from Serbia.
It is mandated to enforce the rule of law and supervise its police, customs and judiciary. EU judges and prosecutors have the power to step in and take on cases that the local judiciary is unable to handle because they are too sensitive.