I don't know any more about this case than Meatpie tells us, but I'd bet a week's pay she killed him because she could no longer tolerate his physical abuse of her when he was drunk (i.e. all the time).
Alex, I think your speculation is quite likely.
In police work, anytime a spouse disappears, the surviving spouse is automatically a suspect. If the missing spouse is known to be abusive, then there is in addition a clear motive. There, the police might have to
exclude an abusive spouse, knowing what we know about the bleak social situation in Putin's Russia.
What led the police to dig up the back yard? We can see the grave was shallow, and the body is fresh.
Really fresh, in fact. Everyone is in short-sleeves, so it is warm out, which means the weather didn't help preserve the body. It's
hard to conceal fresh-turned earth, at most only several days old.*
It's interesting that the ax (presumed murder weapon) is broken. She must have hit him
hard. Which speaks to your original point: she probably snapped,
"I'm not going to take it anymore, motherfucker!"
Burying his body in the back yard was a move of desperation, and also of course quite stupid. Too bad she didn't know about CDG. I'm sure lots of folks here could have given her
much better tips.
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* OTOH, why in the world did they have to dig up so much of the backyard to find his body?
Corpse detecting dogs must be in short supply in the Russian Police.