The May 2009 attack at the temple of the Dera Sach Khand sect had triggered widespread violence in India's northern states of Punjab and Haryana, leaving three dead and dozens hurt.
After nearly 11 hours of deliberations, the jury found main defendant Jaspal Singh guilty of shooting to death deputy sect leader Sant Rama Nand. The Indian-born man received a life sentence, Austrian press agency APA reported.
He was also convicted of attempted murder in the attack, in which sect leader Niranjan Dass and a local preacher suffered gunshot wounds and more than 12 others were injured. Nand and Dass were visiting the temple on a tour of Europe.
The verdict did not immediately enter into force, as Singh's lawyer said he would appeal.
Singh had claimed that he could not recall the attack, because sect members had severely beaten him on the head during the incident.
Although the five other Sikhs also said they did not remember much of that day, they made clear during the trial that they disapproved of the liberal Dera Sach Khand, because its followers venerate religious leaders in addition to Sikh holy scripture.
Four were convicted of aiding the murderer and were sentenced to between 17 and 18 years behind bars, while one was found guilty of attempted coercion and received a 6-month sentence.
The prosecutor had alleged that some of the men had travelled to Vienna from Barcelona in Spain with the aim of carrying out their crime.
The juror's job was made difficult not only by what the prosecutor called "collective amnesia" on the side of the defendants, but by a similar lack of memory displayed by sect members. Witnesses were unable to say exactly which one of the accused had done what in the temple.
But Singh's DNA was found on the murder weapon, and gunshot residues were found on his body. The court also found it had enough evidence that the other men had used sharp daggers to stab sect members.
Sikhs and Dera Sach Khand followers are not only divided over religious rules but also by their social heritage.
The sect mostly has followers among the Dalit, or low-caste Sikhs.
According to historians, groups like Sach Khand arose from a feeling of discrimination among Dalit converts to Sikhism.
Vienna: Six radical Sikh men received heavy prison sentences on Tuesday in Vienna for their involvement in the killing of a senior Indian sect leader last year in Austria's capital, media reported.
First Published: Tuesday, September 28, 2010, 09:04