The incident occurred on November 17 but has only recently come to light after Life News published a CCTV recording of the dramatic shooting on November 21.
The footage shows two young men sitting on a carriage on Moscow's Serpukhovsko-Timiryazevskaya line when the attention of one of them seems to be attracted by another passenger.
A brief exchange follows before the other passenger appears on screen and the man stands up to confront him.
Then, events suddenly escalate in a bizarre fashion.
In the blink of an eye, the man pulls out a gun and shoots the other passenger in the stomach, kicks him, and then shoots him in the head.
As other surrounding passengers quickly move to the other end of the carriage, the shooter and his companion calmly wait for the train to pull up at the next station.
The man accompanying the assailant also pulls out a pistol and seems to brandish it at the stricken passenger before he and his cohort disembark when the train pulls up at Nagornaya station.
The footage ends with the victim examining his wounds as blood drips from his body onto the floor of the train.
WATCH: A Bizarre Gun Attack On The Moscow Subway
The wounded man has since been identified as Hashim Latipov, who originally hails from the North Caucasus Republic of Daghestan.
Luckily, Latipov's wounds are not considered life-threatening as it transpires that the realistic-looking weapon used in the attack is a so-called "trauma gun," a type of air pistol that is popular in Russia and often used for self-defense purposes.
Nonetheless, he has still had to undergo several operations and the shot to the head, which hit him in the upper jaw, will probably leave him scarred for life.
In an interview with the Azerbaijani news website gapp.az, Lapitov claimed he had no idea why the attack occurred.
"We just locked eyes..." he said. "I turned away, but he kept looking. And it was such a contemptuous look. He looked like a psycho; like he wanted to kill someone. I was sitting there and I asked him 'What are you looking at?' He immediately exchanged a few words with his friend. When I approached them, he stood up, silently took out a gun, and started shooting.
Although the faces of the attackers are clearly visible in the CCTV recording, police investigators have still not succeeded in identifying them.
No motive has been ascribed to the attack, but Moscow is a city riven with racial tensions and unprovoked attacks on racial minorities, particularly economic migrants from the Caucasus region, are not uncommon.
-- Coilin O'Connor with contributions from Merkhat Sharipzhanov