A 56-year-old YouTuber who killed another YouTuber was sentenced to a lifetime in prison on Wednesday, after which he shouted "thank you" for unexplained reasons.

Busan District Court found the defendant surnamed Hong guilty of retaliatory murder, rejecting his claims that he had never intended to kill the victim. The court pointed out that it was a planned crime, and that the defendant stabbed the victim 12 times to inflict critical wounds.

South Korea's Criminal Act stipulates that those found guilty of murder are to be punished by from at least five years in prison to death penalty, but the Act on the Aggravated Punishment of Specific Crime says the minimum punishment for a retaliatory murder must be at least 10 years in jail.

The defendant attacked the victim at around 9:52 a.m. on May 9 in front of the Busan District Court in Yeonje-gu, Busan. The incident was broadcast via the victim's YouTube channel.

The two YouTubers had been involved in a feud that culminated in over 200 legal cases between them. The victim was en route to a court hearing on the day of the attack, in which he was slated to testify in his bodily damage accusation against Hong.

Hong claimed that he attacked the victim out of anger from the victim insulting him and his girlfriend.

"(The defendant) saw the victim fall to the ground after the initial attack, yet decided to relentlessly attack him. Considering his past records of violent crimes, it is necessary for him to be permanently isolated from society," the court said in the verdict.

After the verdict, the defendant clapped and shouted out, "Thank you," while yelling profanity to the bereaved family of the victim who were present in court.