On May 27, 1985, the trial against Sergei Antonov begins. On March 29, 1986, the Rome Criminal Court, under the presidency of Severino Santiapicchi, issued an acquittal "due to lack of evidence" against the Bulgarian citizens Sergei Antonov, Todor Aivazov and Zhelyo Vassilev. On the same day, BTA was authorized to declare the satisfaction of the Bulgarian public with the decision. "The verdict is an admission that Bulgarians had nothing to do with the assassination attempt on Pope John Paul II", the declaration says.
In 1981, he was deputy director of the BGA "Balkan" bureau in Rome when on May 13 this year, an assassination attempt was carried out against the head of the Roman Catholic Church, Pope John Paul II.
Antonov was arrested on November 25, 1982 in Rome on charges of complicity in the assassination attempt. He was attacked by Turkish terrorist Mehmed Ali Agca, a member of the Turkish terrorist organization "Grey Wolves", who was captured at the scene of the crime and later sentenced to life imprisonment for shooting the pope in "St. Peter".
On November 27, 1982, BTA released an official statement in which it defined Antonov's arrest as "completely illegal, arbitrary, absolutely unjustified".
On December 1, 1982, an order was issued by the investigating judge Ilario Martella for the arrest of two more Bulgarian citizens - Todor Aivazov (head of the financial service of the Bulgarian embassy in Rome) and Zhelyo Vassilev (former secretary of the military attaché).
At the end of December 1983, at the insistence of doctors, Sergei Antonov was released from prison and placed under house arrest, as Italian doctors noted his deteriorating mental condition and recommended a milder measure. Not long after, at the request of prosecutor Antonio Albano, Antonov was returned to prison.
On March 28, 1984, in a letter to Pope John Paul II, the Bulgarian Patriarch Maxim noted that the innocence of Sergei Antonov was indisputable not only for the Bulgarian people, but also for all open-minded people. On behalf of the Holy Synod of the Bulgarian Orthodox Church, Patriarch Maxim asked the Pope to "express his deep conviction in Antonov's innocence." On April 30, 1984, in his response to the Bulgarian Patriarch, Pope John Paul II informed that, in response to the steps taken by the Holy See, the Italian government was taking action to expedite the procedure concerning Sergei Antonov. On April 1, 1986, Antonov returned to Bulgaria. On April 5, 1991, Bulgarian Ambassador Ognyan Pishev officially announced in the United States the decision of the Bulgarian government to grant an international independent commission unlimited access to the archives in Bulgaria related to the assassination attempt on the Pope. On May 24, 2002, during his official visit to Bulgaria, during his meeting with President Georgi Parvanov, Pope John Paul II states that he never believed in the so-called "Bulgarian trace" in the assassination attempt against him in 1981.