Putin's old spy agency is a prime suspect for taking out Prigozhin's plane

• Russia's FSB appears the most likely party in the apparent death of Prigozhin.
• UK sources told the BBC the agency probably targeted the plane Prigozhin was apparently on.

Russia's main security and spy agency, once led personally by Vladimir Putin, is emerging as a prime suspect in the plane crash that appears to have killed Wagner mercenary group Yevgeny Prigozhin.

UK defense sources told the BBC that the FSB is the party most likely to have targeted the plane, adding some specificity to the widespread presumption that Putin's administration assassinated Prigozhin.

Prigozhin is presumed dead after a private jet on which he was listed as a passenger crashed in Russia's Tver region outside of Moscow on Wednesday.

Putin and the FSB have a long history. Putin was made the leader of the FSB in 1998, and was then made Russia's deputy prime minister less than a year alter.

Before his time as a politician, Putin had a long career in the Soviet Union's KGB agency, which eventually became the FSB after the fall of communism.

The BBC also noted that the FSB is known to be unwaveringly loyal to Putin.

It has been accused before in attacks on enemies who earned Putin's disdain: the poisoning of Putin critic and opposition politician Alexei Navalny and the assassination of former Russian spy and Kremlin critic Alexander Litvinenko are two examples.

Ultimately, it's not clear what happened to Prigozhin yet.

But the leader of the mercenary group, which fought for Russia in its invasion of Ukraine, had been feuding with Russia's military leadership for months and publicly criticizing its performance. This culminated in an uprising in June, with his troops taking over a key military base in southern Russia and starting to march towards Moscow.

A peace deal was struck but experts, as well as the head of the CIA, had warned that Prigozhin could face revenge from Putin.

Germany's foreign minister said the crash seemed to fit "this pattern in Putin's Russia: deaths, dubious suicides, falls from windows, all which remain unclarified – that underlines a dictatorial power system that is built on violence."

She said "It is no accident that the world immediately looks at the Kremlin when a disgraced former confidant of Putin suddenly, literally falls from the sky two months after he attempted a mutiny," according to The Guardian.

White House National Security Spokesperson Adrienne Watson said that if Prigozhin's death is confirmed "no one should be surprised."

Experts told Insider that three likely scenarios for Prigozhin's death are that Putin ordered it, someone else ordered it, or that Prigozhin didn't actually die and faked his death.

Flight-tracking data showed that the plane was showing no signs of trouble before it had a sharp plummet in the last 30 seconds of its flight, tracking service Flightradar24 told Reuters.