At least five prominent Russian businessmen have reportedly died by suicide since late January, with three of them allegedly killing members of their families before taking their own lives.

Four of the dead men were associated with the Russian state-owned energy giant Gazprom or one of its subsidiaries.

CNN's calls to Gazprom have not been returned.

A top executive at Gazprom was found dead in his cottage in the village of Leninsky near Leningrad on January 30, 2022, according to Russian state media RIA Novosti.

RIA reported that a suicide note was found at the scene and that the investigators were investigating the death as a suicide. Russian national broadcaster RenTv has identified the man as Leonid Shulman, the head of transport at Gazprom Invest.

Just a month after that, another top executive at Gazprom was found dead in the same village. Alexander Tyulakov was found dead in his garage on February 25, according to Novaya Gazeta, an independent Russian newspaper. Novaya Gazeta reported he died by suicide.

Leonid Shulman, the head of transportation at Gazprom Invest.

CNN has asked Russia's Investigative Committee for comment on the two cases but has not received a response.

Mikhail Watford, a Ukrainian-born Russian billionaire, was found dead in his home in Surrey, England on February 28.

Surrey Police told CNN that the death is being investigated by the coroner, who said a hearing will be held on July 29.

Another Russian businessman, Vasily Melnikov, was found dead alongside his family in Nizhny Novgorod in late March, according to the Russian newspaper Kommersant.

Melnikov owned MedStom, a medical supplies company. According to Russia's Investigative Committee, a 43-year-old man, his wife, 41, and two children aged four and 10 were found stabbed to death on March 23.

The committee did not name Melnikov, but the ages of the dead and the location of the incident match the Kommersant report.

The regional branch of the investigative committee has not updated the status of its investigation and did not return CNN's request for comment. At the time of the incident, in March, it said there "were no signs of unauthorized entry into the apartment," and "knives were found and seized."

"[Investigators] are considering several versions of what happened, including the murder of the children and wife by the head of the family, followed by self-inflicted death," the committee said.

And earlier this month, two more Russian businessmen died in apparent murder-suicide incidents.

Vladislav Avayev, the former vice-president of Gazprombank, was found dead with his wife and daughter in his Moscow apartment on April 18, according to Russian state news agency Tass.

Citing a source in law enforcement, Tass claimed authorities were investigating the Avayevs' deaths as a murder-suicide.

Yulia Ivanova, a representative of the Investigative Committee for Moscow, was quoted by Tass as saying that a relative discovered the Avayevs' bodies after being told by the family driver and the nanny that they could not contact them on the phone or get into the apartment, since the door was closed from the inside.

Igor Volobuev, former VP of Gazprombank, who has recently left Russia for Ukraine, told CNN he did not believe Avayev killed himself.

"His job was to deal with private banking, that means dealing with VIP clients. He was in charge of very large amounts of money. So, did he kill himself? I don't think so. I think he knew something and that he posed some sort of risk," Volobuev told CNN.

Just a day later, on April 19, Sergey Protosenya, former executive at the gas producer Novatek, which is partially owned by Gazprom, was found dead north of Barcelona. The bodies of his wife and daughter were found nearby, an official source close to the investigation told CNN last week.

Protesenya, his wife and daughter were found at their home in Lloret de Mar, a Mediterranean resort near Barcelona.

The bodies of the two women, showing signs of having suffered violence, were found inside the family's luxury home, and the body of Protosenya was found in the garden outside, according to the source. The case is being investigated as a double-murder and subsequent suicide in a domestic violence case.

Speaking to the Daily Mail, Protosenya's son questioned the version of the events, suggesting instead his father was murdered.

'He loved my mother and especially Maria my sister. She was his princess. He could never do anything to harm them. I don't know what happened that night but I know that my dad did not hurt them," said Fedor Protosenya, who was at the family home in France at the time of the incident.

Catalan police in the province of Girona, where the town of Lloret de Mar is located, told CNN on Friday that "the hypothesis continues to be a domestic violence case despite the statements by the son."

"The Catalan police have taken statements from the son. Other hypotheses have been ruled out. Also ruled out was a triple homicide," the police's press official told CNN.

"That this was the work of the Russian mafia? Well, no," the official added.

Novatek, Protosenya's former employer, said he was "a wonderful person and a wonderful family man."

"Unfortunately, there have been speculations on this topic in the media, but we are convinced that these speculations are not related to reality. We hope that the law enforcement agencies of Spain will conduct a thorough and objective investigation and sort out what happened, " the company said in a statement. (CNN: Excluding headline)

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