Karina's savagely beaten and slashed body was found in a house in Novosobirsk with 25 stab wounds. Picture: Social media

Killer Mark Konkov, 17, has been sentenced to nine years in a penal colony for stabbing to death his former girlfriend in a 'murder of special cruelty'.

The sentence - a year below the maximum for an offence committed when the killer was 16 - came after a public campaign for justice to be done, amid fears the case would be hushed up.

In outbursts in court, the tycoon and his wife Natalia was quoted as saying Karina should not have come to their house because 'she was not from our social strata'.

Karina Zalesova's body was found on 28 August in Igor Konkov's house. Pictures: Social media

The girl had gone to see construction tycoon Igor Konkov's son after he threatened to kill himself if she did not come to him. Karina went out without telling her parents where she was going.

Her cell phone did not answer, and was then switched off, and her parents reported her missing to police. Later her savagely beaten and slashed body was found in a house in Novosobirsk with 25 stab wounds.

He has first beaten her with his fists and a wooden figurine, then grabbed the knife, stabbing her a dozen times in the throat, and 13 times to her face.

Initially Konkov was detained but then put under house arrest, sparking protests in Novosibirsk, Moscow and St Petersburg that the case could be hushed up. The protests followed the victim's father posting a message online that he feared Konkov's wealthy could exert influence on the law enforcement process.

Killer Mark Konkov, 17, has been sentenced to nine years in a penal colony for stabbing to death his former girlfriend in a 'murder of special cruelty'. Pictures: Social media, NGS.ru

Sergey Zalesov wrote: 'He [Mark] had a very rich family. We were told: 'It will be not so easy for you, if you do not talk to media and get publicity.' We fear very much that the case will be hushed up. I want him to answer to the law for what he's done.'

After the initial protests, the teenager was removed from house arrest and held in detention. Regular rallies were held to keep a public focus on the case.

Psychiatric tests in Moscow on Konkov found personality disorders and sadistic inclinations but deemed he was 'sane' when he killed Karina.

The case was reclassified from 'Murder' to 'Murder with special cruelty'.

Konkov senior argued in court that his son and the girl had a suicide pact, but that only she died. Foresnic evidence indicated the girl had defended herself against a vicious attack, the court heard.

Regular rallies were held to keep a public focus on the case. Pictures: Social media, Alyona Martynova

Konkov junior eventually agreed to give evidence and rebuffed his father's version of a suicide pact. 'I just killed her and that's all,' he said.

The case was heard in closed session but a relative of Karina, Maria Grebenkina, who attended the court, was quoted saying: 'At today's hearing Konkov's parents finally lost their human face.

'Konkov's mother, Natalia, claimed: 'Does anybody think that I would allow my son to be close with this girl? She was not from our social strata. If this girl knew it is not good to come to somebody's house just like that, she would be alive.'

Natalia Konkova (top) and Igor Konkov (bottom) argue that their son is not guilty. Pictures: Tayga.info, Tekhstal

Grebenkina continued: 'The father was outraged, he shouted: 'There was no special cruelty. I saw her body and she looked normal, she was just dead. We are from different strata, no one invited her to our house, she came by herself.'

When he was reminded that she came because his son threatened to commit suicide if she did not appear, he said: 'Now other girls will know how to feel pity.

She would be alive if she did not come. I believe my son is not guilty.'

Konkov will be put in an adult penal colony once he turns 18.