Police said they had arrested a 27-year-old man suspected of shooting a 42-year-old fellow audience member who later died of his wounds.
The conflict took place as the credits rolled during a screen of the Oscar-nominated film "Black Swan", according to police in the Baltic state.
Witnesses told the Latvian news agency Leta that it arose over how loudly the deceased man was eating his popcorn.
Gun-crime is relatively rare in Latvia, a European Union nation of 2.2 million.
The shooting occurred on Saturday evening in the central multiplex cinema in the Latvian capital, Riga, at the end of the psychological thriller about a ballet dancer who loses her mind succumbing to pressure to perform."
Yikes! I normally just do the slight head turn and eye roll, maybe a "c'mon man, cut it out" shrug...