TLDR (SPOILERS);

He was the co creator and him and the main creator couldn't make money from the title because it was made in Russia on work equipment. They later moved to the US and started a new company. The main creator later got ownership of the Tetris title when the copyright expired and so he started a company with it. The co-creator stayed at the other company, which was eventually floundering. He used a knife and hammer to kill his wife, 12-year old son, then himself. Two weeks later the floundering company was offered an influx of money.