LONDON — The teenager accused in a stabbing attack that killed three girls at a Taylor Swift-themed dance class in England has been charged with causing the deadly ricin poisoning and now faces a terrorist offense, police said Tuesday.

Merseyside Police said 18-year-old Axel Rudakubana, who is accused of killing three girls and stabbing 10 others in July, produced the deadly poison ricin which was later found in his home.

Ricin is derived from the castor plant and is one of the deadliest toxins in the world. It has no known vaccine or antidote and kills cells by preventing them from making proteins.

Rudakubana also had an al-Qaida jihad training manual, Police Chief Serena Kennedy said.

Police pointed out that while the production of ricin was considered a terrorist offence, the knife attack in July was not classified as a “terrorist incident”, which would require a motive to be known.

Rudakubana, who police said was born in Wales, already faced three murder charges in the July deaths of Alice Dasilva Aguiar, 9, Elsie Dot Stancombe, 7, and Bebe King, 6, in the town on seaside Southport in North West England.