Moscow's Investigative Committee said it had detained a 20-year-old man on suspicion of seven murders and a 25-year-old woman believed to have taken part in four of the killings.
"The detained man said he committed the murders with the aim of 'cleaning up' the city," investigators said.
The man is suspected of committing the murders in Moscow, "choosing as his victims homeless people who were fond of drinking alcohol" and carrying out the crimes in lonely places at night, the investigators said in a statement.
The killers' second alleged victim was a man who lived in a communal flat but spent much of his time drinking in parks, Life News reported, while the rest of their victims were actually homeless.
Also Read
The couple were captured after they knifed a street cleaner, who survived and managed to identify them to police, Life News added in a report.
Russia does not issue official statistics about the number of homeless people but is believed to have three to four million out of an official population of more than 140 million.
In Moscow, homeless people often huddle at mainline railway stations or sleep in metro trains.
In 2007, a notorious serial killer, Alexander Pichushkin was jailed for 48 murders in Moscow's Bitsevsky Park.