In the early 00ies it was crazy conspiracy theories to suggest FSB planted bombs in Moscow in 1999 to re-start the Chechnya war so that Putin could enter his first presidential election as war President. in 2007 this was entered into testimony in the United States House of Representatives:

Russian apartment bombings - Wikipedia, the free encyclopedia

"With Yeltsin and his family facing possible criminal prosecution, however, a plan was put into motion to put in place a successor who would guarantee that Yeltsin and his family would be safe from prosecution and the criminal division of property in the country would not be subject to reexamination. For "Operation Successor" to succeed, however, it was necessary to have a massive provocation. In my view, this provocation was the bombing in September, 1999 of the apartment building bombings in Moscow, Buinaksk, and Volgodonsk. In the aftermath of these attacks, which claimed 300 lives, a new war was launched against Chechnya. Putin, the newly appointed prime minister who was put in charge of that war, achieved overnight popularity. Yeltsin resigned early. Putin was elected president and his first act was to guarantee Yeltsin immunity from prosecution."^[153]

I have always had the shift connected with Putin taking back state control over oil and gas, but I fail to pinpoint any particular event.