A lawyer who shot another man dead in a Riga cinema over an argument about munching too loudly on popcorn has been sentenced to 17 years in prison.

Nikolajs Zikovs was convicted of aggravated murder for shooting banker Aigars Egle, who was with his young daughter, after telling the victim to be quiet during a screening of the film "Black Swan" on February 19 last year.

Zikovs, 29, told Riga District Court on Tuesdayy that he was acting in self-defence when he shot the unarmed Egle three times.

Witnesses said Zikovs had himself made several disruptions during the film, then took issue with Egle over how loudly the victim had been eating popcorn, even though the film's end credits were rolling.

Egle had a gun licence, local news agencies said.

The killer described himself as a reasonable man and said Egle should have been more polite.

Egle, a 43-year-old father of four, was a senior banker with state-owned Citadele bank and the case sparked widespread revulsion in Latvia with Zikovs being seen as an emotionless and arrogant figure obsessed with carrying a gun.