Damian Kudryavstev, the editor of the Moscow Times newspaper, confirmed the news on Facebook.
After being given a suspended sentence for another count of fraud in 2006, he fled to the United Kingdom to seek political asylum and became a critic of Russian President Vladimir Putin.
Police said the death was being treated as unexplained, adding that the counterterrorism team would lead the investigation "as a precaution because of associations that the man is believed to have had".
In the 1990s, Glushkov was the deputy director of LogoVaz, a auto sales company founded by Boris Berezovsky, and "Aeroflot", Russia's flagship airline and largest passenger carrier. Glushkov was subsequently accused of fraud, larceny and money laundering overseas.
Five years on, the same questions will be asked of his own death.
He was released in 2004, before he was granted asylum to the UK.
Police, meanwhile, said the investigation of who poisoned Skripal and his daughter, Yulia, will last many weeks and that they are not ready to identify any persons of interest in the inquiry. Mr Berezovsky lost the £3.2bn claim and was found by a judge to have been "deliberately dishonest". Meanwhile, Berezovsky disappeared from public life. His friends were not so certain, with a coroner recording an open verdict.
Andrei Borovkov told Russian media outlets Tuesday that his client, Nikolai Glushkov, has died, but said he was unaware of the time and circumstances.
"I'm definite Boris was killed". I have quite different information from what is being published in the media.
Russian media have contacted those individuals closest to Glushkov to find out the reason behind his death.
"Boris was strangled. Either he did it himself or with the help of someone". A close friend of the deceased said to the Russian radio station Govorit Moskva that he may have died of AIDS, adding that Glushkov never hid his homosexuality.
He later told the Guardian: 'Too many deaths [of Russian emigres] have been happening'.
Nikolai Glushkov was arrested and put in jail. In 2013 Glushkov emailed a friend: "I have a lot of new facts that are of great interest".