Axel Rudakubana, 18, who is charged with murdering three girls and stabbing 10 other people in July, produced the deadly poison ricin that was later found in his home, Merseyside Police said on Tuesday (early Wednesday AEDT).
Police also found he had a computer file with an Al-Qaida training manual titled “Military Studies in the Jihad Against the Tyrants”.
Ricin is derived from the castor bean plant and is one of the world’s deadliest toxins.
It has no known vaccine or antidote and kills cells by preventing them from making proteins.
Police stressed that the July attack has not been classed as a “terrorist incident”, which would require a motive to be known.
Rudakubana, who police said was born in Wales, already faced three counts of murder over the July deaths of Alice da Silva Aguiar, 9; Elsie Dot Stancombe, 7; and Bebe King, 6; in the seaside town of Southport in north-west England.
He also has been charged with 10 counts of attempted murder for the eight children and two adults who were injured.
The stabbings were used by far-right activists to stoke anger at immigrants and Muslims after misinformation spread on social media identifying him as an asylum seeker and misreporting his name.
Violence spread from Southport and led to rioting across England and Northern Ireland that lasted a week.