These are all the Russian oligarchs who have died suddenly, some in suspicious circumstances, in recent months

• At least seven Russian oligarchs have been found dead in recent months.
• Some have died in suspected murder-suicides along with their wives and children.

Last week Russian oligarch Sergey Protosenya was found dead in Spain alongside his wife and daughter. The local police's working theory is that it was a murder-suicide.

But his son has publicly rejected the theory, telling MailOnline that his father "is not a killer."

The day before, another oligarch, Vladislav Avayev, was found dead in Moscow along with his wife and daughter in another suspected murder-suicide.

The two men are the latest in a series of oligarchs who have turned up dead in recent months in apparent suicides, many of whom had links to major Russian gas companies.

"In all cases, there are widespread suspicions that the deaths may have been staged as suicides, but who did this and why?" Grzegorz Kuczyński, director of the Warsaw Institute's Eurasia Program, told Fortune.

Here is the full list:

Sergey Protosenya

Millionaire oligarch Sergey Protosenya was found hanging in a rented luxury villa in Spain on April 19, according to Spanish TV channel Telecinco. His wife and 18-year-old daughter were also found dead in the apartment with stab wounds.

The Catalan police body investigating the deaths said their primary working theory is that it was a murder-suicide, a spokesperson from Lloret De Mar's town hall previously told Insider's Mia Jankowicz.

Protosenya, 55, was a former employee of Novatek, a major Russian natural gas production company.

Novatek has cast doubt on the theory that Protosenya killed his family, calling him an "outstanding person and a wonderful family man."

His surviving son Fedor has similarly rejected the murder-suicide theory, telling MailOnline that his father "could never do anything to harm" his mother and sister.

"I don't know what happened that night, but I know that my dad did not hurt them," Fedor said.

Protosenya had a personal fortune of more than $433 million, according to Telecinco.

Vladislav Avayev

Vladislav Avayev, 51, was found dead of a gunshot wound in his Moscow apartment on April 18, along with his wife and 13-year-old daughter, Russia's state-run TASS news agency reported.

He was the former vice president of Gazprombank, a privately-owned subsidiary of Russian energy giant Gazprom.

The Avayevs' apartment was locked from the inside, and investigators are prioritizing the theory that he shot his wife and daughter before killing himself, TASS reported.

Vasily Melnikov

Vasily Melnikov was found dead in his apartment in Nizhny Novgorod, Russian newspaper Kommersant reported on March 23.

The billionaire was stabbed to death, as were his wife and two sons, aged 10 and 4. Knives, believed to be the murder weapons, were found at the scene, the outlet said.

The police are investigating the theory that Melnikov killed his family and then himself.

Melnikov owned Medical equipment supply company MedStom, and Ukrainian outlet Glavred reported that they had been suffering significant losses due to Western sanctions.

Another theory, according to Glavred, is that the businessman was murdered following a conflict with a former business associate, and he had taken extra security precautions.

However, Kommersant reported no signs of forced entry into the apartment.

Mikhail Watford

Ukrainian-born oligarch Mikhail Watford was found hanged in the garage of his home in Surrey, England, on February 28, according to the BBC.

Watford, in his 60s, was born in then-Soviet Ukraine and made his fortune in oil and gas. He moved to the UK in the early 2000s with his Estonian wife, the outlet said.

Surrey Police said that the investigation was ongoing, but there were not believed to be any suspicious circumstances "at this time," the BBC said.

Alexander Tyulyakov

Alexander Tyulyakov was found hanged in an apartment's garage near St. Petersburg on February 25, according to the Russian newspaper Novaya Gazeta.

Police told Gazeta that they found a suicide note next to his body.

Tyulyakov, 61, was an executive for Russian energy giant Gazprom, and the company is also investigating his death, per Gazeta.

Gazeta cited a report from Russian outlet Fontanka.ru that claimed Tyulyakov was seen having been badly beaten on the eve of his death.

Leonid Shulman

Another top Gazprom executive, Leonid Shulman, was found dead in a cottage in the same village in January, before Russia began its invasion of Ukraine, according to Russian media company RBC.

A suicide note was found near his body, which said that he did not want to be a "disabled person" or a "burden" to his family and complained about unbearable pain in his broken leg, according to Gazeta and Russian outlet 78.ru.

Shulman had been on sick leave due to a leg injury, 78.ru reported.

However, Gazeta said investigators were questioning the note's authenticity, adding that Shulman would have been able to afford high-quality pain medication.

Alexander Subbotin

Alexander Subbotin, a former top executive of Russian oil company Lukoil, was found dead in a shaman's house in Mytishchi, Russia, according to Russian news agency TASS.

Subbotin suffered a heart attack, authorities told TASS, but an investigation is ongoing.

A source told TASS that Subbotin had arrived at the house in severe alcohol and drug intoxication the day before and was found dead in the shaman's house in a room used for "Jamaican voodoo rituals."

An unverified telegram channel Mash claimed that Subbotin was there to get a hangover cure in the form of toad venom and has been friendly with the shaman and his wife for some time, The Independent reported.