The couple, named in local media as Dmitry Baksheyev, 35, and his wife Natalya, 42, are suspected of killing as many as 30 people over the past two decades while living at a military academy in south-east Russia.
Recipes and video lessons for cooking human meat were reportedly found in their dormitory, alongside body parts.

Investigators were tipped off after road workers found a phone belonging to Mr Baksheyev, which included selfies of him with a severed hand and other body parts belonging to a woman.
Mr Baksheyev is believed to have killed the woman and cut her up after the couple quarreled with her during a drinking session three days earlier, according to a statement by the Krasnodar investigative committee.

Local media published a photograph of what appeared to be the man with a human hand in his mouth.
Investigators later discovered fragments of a human body in a salt solution and frozen meat of an unknown origin in their room in a dormitory at the Krasnodar military aviation academy, where Mrs Baksheyev had reportedly been employed.

Among the finds was a jar with the preserved hand that the husband had taken a selfie with, state news agency RIA Novosti reported.
A search also uncovered remains of the dead woman in a nearby basement.
Investigators have announced a murder investigation into the death of the woman.

Mr Baksheyev claimed he had simply found the body parts and photographed himself with them, investigators said.
RIA Novosti later quoted a source as saying he had admitted to killing the woman as well as a previous victim in 2012, and reports said that the pair had been connected to at least seven killings.

Komsomolskaya Pravda newspaper published a blurred-out photograph, which it said was taken in 1999 and found in the Baksheyev home, showing a cooked human head on a platter with mandarin oranges.
Phones belonging to alleged victims were also discovered in their room, the newspaper cited a law enforcement source as saying.

Entrepreneur Vitaly Yakubenko told local media outlets Natalya had interviewed for a chef job at his restaurant in 2010, asking several questions about where he bought his ingredients while Dmitry waited outside.
"She kept asking everything about meat, whether I wanted to buy it cheaper," Yakubenko told Komsomolskaya Pravda. "Apparently she wanted to sell human meat in my bistro."