[Alexei Navalny’s] body reacted differently to a fast-acting substance that was rapidly excreted from the body, which his friend Maria Pevchikh gave him. According to a source, she is also an employee (undercover agent) of the [British Secret Intelligence Service] MI6. So, it was the work of Maria Pevchikh.
These substances have been in Russia for a long time. They don’t even need to be brought to Russia. They have been kept in the embassies of different countries since the 90s. And there are enough of them for many years. Several people have already died from these substances. However, it will never be possible to prove that it was precisely the poisoning.