The body of Vladislav Avayev, former vice president of Russian lender Gazprombank, was found with those of his wife and daughter in the family’s Moscow apartment last week, Russian state-controlled news agency TASS reported on April 18.

Gazprombank is Russia’s third largest bank, and services energy giant Gazprom, the country’s major exporter of natural gas.

TASS said preliminary evidence suggested the deaths were the result of a murder-suicide, alleging Avayev was responsible, and adding that a police investigation was under way.

Avayev was a former Kremlin official, according to Western media reports.

On Wednesday, Spanish broadcaster Telecinco reported that Sergey Protosenya—a former executive at Novatek— died in a remarkably similar manner. Protosenya, his wife, and his 18-year-old daughter were all found dead in their villa in the upscale Spanish coastal town of Lloret de Mar.

Novatek is Russia’s largest independent producer of natural gas.

According to local law enforcement, Telecino reported, initial investigations appeared to show that the family’s deaths had resulted from a murder-suicide.

But Spanish news outlet El Punt Avui later reported that investigators had not ruled out a third party carrying out a triple murder.

Novatek—where Protosenya worked between 1997 and 2015—said in a statement Thursday the company is convinced that speculation about the mysterious circumstances around the deaths, and who may be responsible, “are not related to reality.”

“Sergey Protosenya…has proven himself to be a wonderful person and a wonderful family man,” Novatek said. “We hope that the law enforcement agencies of Spain will conduct a thorough and objective investigation and sort out what happened.”

Previous unsolved cases

The deaths of Avayev and Protosenya and their families come after Russian oligarchs Leonid Shulman and Alexander Tyulyakov were found dead in mysterious circumstances earlier this year.

Shulman, head of Gazprom’s Invest transport service, was found with stab wounds to his wrists, while Tyulyakov was found hanged in a garage.

Both men were found in a luxurious real estate compound of Leninskoye, near St. Petersburg.

The spate of apparent suicides “seem somewhat suspicious,” according to Polish thinktank the Warsaw Institute.

Shulman’s January death came after a probe into his alleged fraud at Gazprom was opened the prior autumn, while Gazprom’s security units arrived at the scene with police following Tyulyakov’s death in February, according to the organization. The Warsaw Institute said in a note on its Russia Monitor site yesterday that Gazprom’s security agency is investigating all four of the deaths.

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

A spokesperson for the Russian government was not immediately available for comment when contacted by Fortune. Gazprom did not immediately respond to Fortune’s request for comment.