The teenager, who arrived in Vienna with his mother and sister in 2013, was taking an AMS German language course so he could catch up with his Austrian peers at school.

A fight broke out between him and the older man, who was also from Afghanistan, over the discussion of music and Islam. The teenager had reportedly told the 31-year-old father-of-two, whose passion was to make music, that he did not listen to music that the Quran does not allow.

A scuffle broke out as a result and the two had to be separated by colleagues and the supervisor.

According to prosecutors, the teenager had then planned to “finish” the other man and returned to the course the next day with two knives, attacking the 31-year-old and stabbing him to death.

The defendant challenges this version of events, however, and says he only brought the knives before he was fearful of his life following threats made by the victim during the fight.

He said when he returned to the course the next day the 31-year-old tried to choke him so he went to stab his hand, but got his stomach instead.

“I want to apologise. I regret that a person was killed,” the defendant told the court on Thursday. “I thought that he would kill me.”

This contradicts statements made by witnesses and the police, however, that suggest the victim neither attacked nor threatened the life of the defendant before he was attacked.

The victim, who leaves behind a wife and two young children, received 17 cuts and stab wounds, including fatal punctures to his lung, stomach, diaphragm, and liver. The teenager fled following the incident but was caught a week later near a motorway in the town of Vösendorf.

The defendant pleaded partially guilty but told the court he was acting in self-defence. If found guilty of murder he could face up to 15 years in jail. The case has been postponed until November.