Two Russian oligarchs with links to major gas companies were found dead in alleged murder-suicide cases that occurred within 24 hours of each other, Newsweek reports.

Gazprombank vice-president Vladislav Avayev, 51, a former Kremlin official, was found dead in his apartment in Moscow along with his wife and teenage daughter. Russian police say that Avayev apparently shot them before shooting himself. The scene was discovered by his adult daughter, Anastasia, on Monday.

On Tuesday, the bodies of former Novatek deputy chairman Sergey Protosenya, 55, his wife, 53-year-old Natalya, and their 18-year-old daughter were found in their mansion in Spain by the couple's teenage son. Police at the scene found said the two women had been stabbed and Protosenya had hanged himself outside the home. Newsweek reports that Spanish law enforcement is investigating whether the killings were the result of a murder-suicide or an organized attack by someone outside the family.

The deaths come about one month after Russian billionaire Vasily Melnikov, his wife, and their two sons were found dead in their apartment in the country's sixth-largest city, Nizhny Novgorod. All had been stabbed to death with knives that were found at the scene of the crime. Russian investigators labeled the incident a murder-suicide, but friends and close relatives of the family reportedly have expressed doubts about this theory.

Last February, two prominent Russians were found dead of apparent suicides: oil and gas magnate Mikhail Watford and Gazprom Deputy General Director of the Unified Settlement Center (UCC) for Corporate Security, Alexander Tyulyakov.

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