A Russian man is facing life in jail for killing at least six people, including his wife and daughter, by adding poison to their food and watching their agonising deaths, Russian television reported on Wednesday.

Vyacheslav Solovyov started inventing poisons to test on humans some six years ago, the Vesti news programme on the official RTR channel reported.

Solovyov has been charged with six murders and four attempted poisonings.

The poisonings have shocked the central Russian town of Yaroslavl and Solovyov has asked for his trial to be held behind closed doors.

The television report said he was afraid that he could have imitators.

"He has pleaded guilty to a majority of the killings, but his motives remain unclear," the television said.

Despite researching the matter in libraries Solovyov failed to produce his own brand of poison. Buying large amounts of poison from a private firm was much easier, television quoted a prosecutor as saying.

His wife, with whom he had lived for 14 years, became his first victim.

"He himself added quick-acting poison to her coffee. Vyacheslav had no doubts this would be an ideal murder," the television report said.

"I myself called an ambulance because I did not want to draw suspicion. Olga died at hospital from what doctors believed was a heart attack," Solovyov said.

After he was arrested, he said it was a feeling of impunity that led him to carry out more poisonings and his 14-year-old daughter Nastya was to become the next victim.

He watched the deadly effects of the poison on his own child's health six months but did nothing to save her despite knowing what antidote would be needed.

"Just for fun, the self-educated chemist started adding small portions of poison to his colleagues' (food) at work and then watched the aftermath," the report quoted a criminal investigation into his case as saying.

"It turned out, once he even poisoned an investigator leading a probe into a brawl in which Vyacheslav had taken part - he threw poison into his glass of water during questioning."

He was caught after he tried to poison a neighbouring family. The death of their little child finally led police to wonder why people surrounding Solovyov were dying.

Thallium, a highly toxic metal used in rat poison and insecticides, was found in the hair of Solovyov's victims.

"He could not even explain why he had been doing this," said his lawyer Sultan Umarov.

Solovyov tried to commit suicide by slitting his wrists and is now facing a new psychiatric examination.

Two previous examinations found him to be criminally sane.