He was a troubled young Soviet Communist Party member in Leningrad. He was a small, thin man, about five foot tall and even as an adult showing the effects of childhood malnutrition. He had difficulty holding a job, and had been reprimanded by the Party for having refused a posting that was not to his liking.
As his troubles grew, he became steadily more obsessed with the idea of "striking a blow." As the end of 1934 approached, he was arrested by the NKVD for loitering around the Smolny. However, he was subsequently released and permitted to retain his pistol, an event that has been pointed at as evidence that he was being used by Soviet dictator Joseph Stalin as a tool.
On the afternoon of December 1, 1934, Nikolaev returned to the Smolny and found his way to the third floor. There he shot Sergei Kirov, the well-liked chief of the Leningrad Communist Party. Nikolaev was subsequently apprehended with the aid of an electrician, Platanov, who was working in the area.
Nikolaev then underwent a complete collapse. He had to be carried away, and when he was interviewed by Stalin the next day, he was almost incoherent. He did not even recognize Stalin, and had to be shown the dictator's official portrait before he would believe he was indeed in the presence of the most powerful man in the Soviet Union.
Because of his fragile emotional state, it was decided not to include him in the show trials. Nikolaev was tried alone and secretly by Vasili Ulrikh, Chairman of the Military Collegium of the Supreme Court of the USSR. He was sentenced to death by firing squad, and the sentence was carried out that night.
There has been some speculation that his motivation in killing Kirov may have been more personal. His wife, Milda Draule, worked at the Smolny and there were rumors that she was having an affair with Kirov. However, the possibility remains that Nikolaev's path was smoothed on Stalin's orders.
Nikolaev's mother, brother, sisters, cousin and some other people close to him were later repressed as well. Milda Draule survived her husband by three months before being herself executed. Their infant son (who was named Marx following the Bolshevik naming fashion) was after his parents' execution taken into orphanage. Marx Draule was alive in 2005 when he was officially rehabilitated as a victim of political repressions, and Milda was also found innocent; but Nikolaev however was never acquitted posthumously.