"He would say that he lost trust in people when his classmates began humiliating him for not being like everyone else", a 15-year-old named as Zlata told the Kremlin-funded RT television of Vladislav Roslyakov.
They described photographs circulating on the internet showing Roslyakov wearing a similar T-shirt to Eric Harris, one of the Columbine killers.
According to a source cited by the RIA Novosti state news agency, Roslyakov had legally acquired a gun licence and passed the necessary psychological tests to do so.
The blast happened at around noon at the school, which is located on a peninsula between the Sea of Above and the Black Sea.
President Vladimir Putin even sought to portray the attack as a "result of globalization"- wider forces that were exporting bad practices into Russian Federation. Russia's Investigative Committee opened a criminal investigation into what it said was an act of terrorism.
Some Russian news reports said the shooter had left his backpack containing the explosive device in the cafeteria and remotely detonated it before he started shooting. Officials said at least 19 were dead.
The attack was then reclassified as a murder case. "That means that all of us, not only in Russian Federation, but in the world on the whole, are reacting poorly to the fast-changing realities".
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"He was walking around and shooting students and teachers in cold blood", said Sergei Aksyonov, the regional leader in Crimea.
The "most of the (victims) are teenagers", the committee said. According to the college's website, it accepts students in the last three grades of school, from the age of 14.
A sombre-faced Putin deplored the attack as a "tragic event" and offered his condolences to the victims' families at a news conference in the southern city of Sochi, where he was having talks with Egyptian President Abdel-Fattah el-Sissi.
Some witnesses said more than one person was involved, with one saying a bomb with shrapnel that went off in the school lunchroom during the siege was set off by a second attacker. In January, two pupils in the city of Perm near the Ural mountains attacked a teacher and her fourth-grade class with knives.
He entered the college in 2015 and got a gun permit and bought a rifle and 150 rounds of ammunition several days before the shooting, 112 reported. The paper said Roslyakov's mother is a Jehovah's Witness - a Christian organisation considered "extremist" and banned in Russian Federation. "I saw people without legs, without arms".
Investigators of Russia's Investigative Committee stand at the college entrance in Kerch, Crimea on October 18, 2018, after a student opened fire at a technical college in the Russian-annexed Crimea city of Kerch.
Until now Russian Federation has been immune from mass school shootings, though earlier in the year there were a number of smaller incidents with no fatalities - three in a week - which were enough to scare authorities that the infection had spread.