One month after then-President Boris Yeltsin plucked a security agency official named Vladimir Putin from obscurity and made him prime minister, an explosion leveled a nine-story apartment building on Moscow's outskirts.
The predawn blast on Sept. 9, 1999, reduced the building to a smoking pile of rubble, killing more than 100 people. A second building, less than 6 kilometers away, was rocked by an explosion on Sept. 13, killing 119.
Days earlier, a car bomb exploded in a small town bordering the war-ravaged region of Chechnya, where reignited fighting was already spilling into neighboring regions. That blast, outside the apartment building in the town of Buynaksk, killed dozens.
It was followed seven days later by a truck bomb that destroyed a nine-story building in another southern city, Volgodonsk, killing 17.
On Sept. 23, Putin asserted terrorists in Chechnya were to blame and ordered a massive air campaign within the North Caucasus region. When asked a day later about the campaign targeting what he called terrorists, Putin responded with the phrase that inaugurated his rise to preeminence.
"We will pursue them everywhere," he said, using a crude slang expression. "Excuse me for saying so: We'll catch them in the toilet. We'll wipe them out in the outhouse."
The statement became a Putin catchphrase, and set the tone for the 20 years of rule that followed.
"Yes, it's one of Putin's original sins," said Sergei Kovalyov, a former lawmaker and rights activist who headed a commission that investigated the bombings in the early 2000s.
The bombings, and the fear they provoked, "were advantageous," he told RFE/RL. "At the time, it was advantageous for him to take control of the country, and to introduce force into the Caucasus, in Chechnya in particular."
Yeltsin and his officials had already endorsed Putin, who was tapped a year earlier to head the country's main security and intelligence agency, the FSB, and also served as secretary of the Security Council.
FILE - Rescuers and firefighters work at the site of a massive explosion that destroyed a nine-story apartment building in the southeastern part of Moscow in September 1999.
In announcing he was elevating a relatively obscure FSB officer to be his head of government, Yeltsin also endorsed him for the presidency, just months ahead of the election.
"I have decided to now name the person who is, in my opinion, able to consolidate society and, drawing support from the broadest political forces, to ensure the continuation of reforms in Russia," Yeltsin said in a televised speech on Aug. 9, 1999. "He will be able to unite around himself those who are to renew Great Russia in the new 21st century."
On Dec. 31, 1999, Yeltsin had resigned and named Putin acting president.
By then, the second war to ravage Chechnya in a decade was raging.
Highly qualified partner
Russia under Yeltsin was reeling.
A year prior to Putin's ascendance, the country had defaulted on its debts, sending the value of the ruble plummeting and wiping out bank balance sheets and international confidence in Yeltsin's fiscal policies, not to mention the savings of many Russians — for the second time in a decade.
Yeltsin's health was increasingly precarious, with reports of his heavy drinking and having undergone at least one round of heart surgery. His family, including his daughter and son-in-law, were dogged by corruption allegations. Yeltsin advisers feared that declining popularity would hurt his allies in December parliamentary elections, never mind the presidential election the following July.
And in Chechnya, five years after the end of the first full-scale war, the region was all but lawless, and a growing number of radicalized fighters from abroad were traveling there to join the fighting.
On Aug. 7, a group of fighters, led by the notorious Chechen commander Shamil Basayev and a Jordanian radical named Ibn Khattab, crossed from Chechnya into neighboring Daghestan and declared holy war. Regional police units, and local villagers, led the response, with little help from better-equipped federal forces; refugees flooded neighboring regions.
Two days later, Yeltsin sacked his government and named Putin prime minister — the fourth prime minister of Yeltsin's tenure.
Putin, who was a KGB officer stationed in East Germany at the time of the Soviet collapse, had served as a mid-level official in the St. Petersburg city government in the early 1990s. He had scant government or leadership experience, no national profile, and no real constituency or base of support among Russians.
In a phone call weeks later with then-U.S. President Bill Clinton, with whom he was on good terms, Yeltsin gave personal assurances.
"I am sure you will find him to be a highly qualified partner," Yeltsin said, according to transcripts released by Clinton's official presidential library.
On Sept. 4, with fighting escalating in Daghestan and along the border with Chechnya, the first of four explosions targeting apartment buildings went off: a car bomb outside a five-story building housing relatives of Russian military personnel in Buynaksk, Daghestan. Sixty-two people died.
The bombing — the first of its sort in post-Soviet Russia — drew wide attention. But for many Russians, it was seen as merely a spillover of the violence already afflicting a distant region.
FILE - Acting President Vladimir Putin shakes hands with workers during his visit to an oil and gas field in Surgut, western Siberia, Russia, March 3, 2000.
Five days later, just after midnight, an explosion rocked a nine-story building located along a leafy bend in the Moscow River just a 30-minute drive from the Kremlin. More than 100 apartments were destroyed. In all, 106 people were killed.
Russians were stunned. Yeltsin ordered a search of thousands of apartments buildings in the city for other possible explosive devices.
Putin declared Sept. 13 a day of national mourning. At around 5 a.m. that same day, another explosion went off in the basement of a brick, eight-story apartment building on Moscow's Kashirskoye Highway, about 6 kilometers south of the previous blast. A total of 119 people were killed.
Three days later, a fourth apartment building was flattened when a truck bomb exploded before dawn in the southern city of Volgodonsk. Seventeen people died.
Together, the bombings panicked the country, and added to further doubts about Yeltsin's leadership. A growing number of Russian security officials publicly accused Chechen terrorists.
On Sept. 23, during a trip to the Kazakh capital of Astana, Putin vowed to take an unflinching line against what he called "bandits" — even when they were in the toilet.
'Sugar sacks' in basement
The day before Putin's "outhouse" comment, on Sept. 22, another incident occurred at an apartment building in the western city of Ryazan.
Two men driving a car with Moscow license plates were spotted carrying sacks into the basement of the building. Police and bomb-disposal experts swarmed the area, discovering they contained a military-grade explosive, and had a detonator and a timer set for 5:30 a.m.
Putin that evening praised the work of investigators for thwarting what appeared to be another bombing attempt.
The next day, three FSB officers were arrested by police in Ryazan and held on suspicion of planting the sacks. But Putin's successor at the FSB, Nikolai Patrushev, declared that the Ryazan incident had, in fact, been a training exercise, and he apologized for scaring an already edgy populace.
"It was not an explosion somebody foiled; it was a security training exercise. The sacks contained only sugar. There were no explosives inside," Patrushev said.
A week later, Putin announced plans for a land invasion of Chechnya using Russian Army units. Russia's air force began using fuel-air bombs — highly destructive weaponry that rights activists say are often used indiscriminately, killing civilians and fighters alike.
By Feb. 2, just over a month after Putin became acting president, and nearly five months after being named prime minister, the Russian Army entered the Chechen capital, Grozny.
The following month, Putin won 53 percent of the vote in the snap presidential election, his first electoral victory.
The official government investigation into the bombings, concluded in 2002, blamed Chechen militants for the attacks.
Independent journalists, researchers, even lawmakers conducted their own investigations and found holes in official statements, including what Kovalyov said was the FSB's shifting explanations for different evidence that emerged.
The fact that the Putin government never allowed a thorough and public investigation, which fully debunked the suspicions surrounding the bombings, was itself problematic, he said.
"A competent, conscientious government should conduct a wide and public investigation in a case like this, with such serious suspicions," Kovalyov said. "In this case, there's been nothing of the sort."
Kovalyov's own commission was stymied in its efforts, when Russian security agents began harassing staff members. Its chief investigator, lawyer Mikhail Trepashkin, was arrested and convicted by a military court for allegedly revealing state secrets. He spent four years in prison. Reporter Yury Shchekochikhin, who also worked for the commission, died after what his relatives believed was a poisoning.
Another investigation was conducted by Aleksandr Litvinenko, a former FSB officer, who worked with historian Yury Felshtinsky and published their initial conclusions in 2001, in the Russian newspaper Novaya Gazeta.
Funded by the exiled Russian billionaire Boris Berezovsky, the findings were compiled into a book called Blowing Up Russia, published in English in 2007, the year after Litvinenko died in London after being poisoned with a highly radioactive substance.
Felshtinsky, who now lives much of the time in the United States, said he believed the bombings were engineered by Russian security agencies to justify a new war in Chechnya, and to help bolster Putin's credibility as a law-and-order leader.
"In 2000, it was clear that the FSB blew up the buildings in order to declare war on the Chechen Republic, and this would result with Vladimir Putin being elected a tough leader," he told RFE/RL.
"After 20 years, nothing has come out that has gone against the narrative," Felshtinsky said. "Nothing has come out that actually goes against this theory. And a lot has come out that, in fact, supports the theory."
John Dunlop, a scholar with Stanford University's Hoover Institution and author of a 2012 book about the bombings, agreed that Putin's rise was cemented by the bombings, and set the tone for his leadership: steely, sober, decisive.
"That narrative, of course, serves to glorify Putin," he said. "And he is, of course, still in power."