LONDON (AP) — The teenager accused in a stabbing rampage that killed three girls at a Taylor Swift-themed dance class in England has been charged with producing the deadly poison ricin and now faces a terror offense for possessing a jihadi training manual, police said Tuesday.

Axel Rudakubana, 18, who is charged with murdering three girls and stabbing 10 other people on July 29, produced the deadly poison ricin that was later found in his home, Merseyside Police said. 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 stabbing attack has not been classed as a “terrorist incident,” which would require a motive to be known.

The stabbing occurred on the first week of summer vacation as girls aged about 6 to 11 participated in a two-hour session led by a yoga instructor and a dance instructor.

Witnesses described hearing blood-curdling screams and seeing children covered in blood running from the studio.

The first officers who arrived were shocked to find so many casualties, Chief Constable Serena Kennedy said.

Rudakubana already faced three counts of murder over the July deaths of Alice Dasilva Aguiar, 9, Elsie Dot Stancombe, 7, and Bebe King, 6, in the seaside town of Southport in northwest 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.

Rudakubana was born in Wales to Rwandan parents, police said. British media reported that he was raised Christian.

Dr. Renu Bindra of the U.K. Health Security Agency said “there was no evidence that any victims, responders or members of the public were exposed to ricin either as part of the incident or afterwards,” and the risk to the public was low. No ricin was found at the site of the stabbing attack.

Ricin is estimated to be 6,000 times more poisonous than cyanide and can be fatal when inhaled, ingested, injected or swallowed. Two millionths of an ounce -- roughly the weight of a grain of salt – is enough to kill an adult.

Several people have gone on trial around the world in recent years charged with attempting to use ricin for murder or terror plots, but examples of its succesful fatal use are rare.

Bulgarian defector Georgi Markov was killed in London in 1978 when a pinhead-sized pellet laced with ricin was injected into his thigh - reportedly by a rigged umbrella.

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This story has been corrected to reflect that the terror charge is related to the jihadi training manual.