The former security chief of Russian oil giant Yukos, Alexei Pichugin, has been sentenced to 20 years in jail for murder and attempted murder.
Yukos has been under remorseless pressure during the past year
Mr Pichugin was convicted last week of carrying out two murders in 2002, as well as an attack on the head of the Moscow mayor's communication service.
He was found guilty of organising the murder of Sergei and Olga Gorin and the attempted murder of Olga Kostina.
Mr Pichugin's lawyers are appealing against his conviction.
Prosecutors had originally asked for a life sentence for Mr Pichugin - who denied all the charges - but reduced this to 20 years after he cooperated with them.
The guilty verdict was the first against a former Yukos official, a number of whom are currently on trial in Russia.
Prosecutors in the trial of former Yukos chief executive Mikhail Khodorkovsky called on Tuesday for the tycoon to be sentenced to 10 years for fraud and tax evasion.
Mr Khodorkovsky and his former colleague Platon Lebedev are standing trial on multiple charges relating to the privatisation of a fertiliser firm in the 1990s.
The pair deny the charges against them. A verdict in the case is expected in May.
Mr Pichugin headed Yukos' security department until his arrest in 2003.
He was accused of organising the murder of the Gorins in 2002 on the orders of Leonid Nevzlin, a shareholder in Yukos and friend of Mr Khodorkovsky.
Mr Nevzlin, who denies any wrongdoing, is wanted by the Russian authorities in connection with the case. He is currently in exile in Israel.
Mr Pichugin was also accused of the attempted murder of Olga Kostina, a one-time adviser to Mr Khodorkovsky who went to work for Moscow's city government.
Lawyers for Mr Pichugin claim there is no proof of the murders since the bodies of the married couple have never been found.
Yukos' main production unit was sold off last year
"Since there were criminal procedural violations in the trial we consider that it was impossible to make such a verdict on Pichugin's guilt," Mikhail Zhidkov, a member of his defence team, said.
They will launch an appeal to the Russian Supreme Court and, if that fails, will consider taking the case to the European Court of Human Rights.
Yukos has been under remorseless pressure from the Russian authorities since Mr Khodorkovsky was arrested in 2003, a campaign which many believe is politically motivated.
It was forced to sell its main Yugansk production unit after being served with a multimillion dollar tax bill and is being sued by state oil firm Rosneft, which ended up owning the business.
Yukos has pledged to fight to recover its lost assets, which it claims have been illegally expropriated, by taking its case to the European Court of Human Rights.
One Russia-based analyst said Yukos was in a "downward spiral" which was likely to result in the eventual sale of its remaining assets.
"To all intents and purposes the Yukos story is over," he told the BBC.
"When the elephant is fallen and there are people sniffing around its carcass, it does not really matter whether there is any meat left or who is going to get this or that part of the body."