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 also 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 ricin that was found in a search of his home, Merseyside Police said. Police also found 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.

Rudakubana had been charged in August with the stabbings in the community of Southport, which police on Tuesday stressed have not been classed as a “terrorist incident” because the motive is not yet known. Police issued the new charges of producing a poison and possessing a terrorism manual on Tuesday.

The stabbing occurred on the first week of summer vacation as about two dozen young girls danced to music by Swift at Hart Space, a community center that hosted everything from pregnancy workshops to women’s boot camps.

Witnesses described hearing screams and seeing children covered in blood running from the studio that was behind a row of homes on a residential street.

Joel Verite, a window cleaner on his lunch break, told Sky News at the time that he was passing by when he saw a woman covered in blood slumped over a car who screamed: “He’s killing kids over there."

Verite saw bloody children in the woman's car and ran in the direction she pointed, entering the studio and being startled to lock eyes with the suspect in a hooded tracksuit holding a knife at the top of the stairs.

“All I saw was a knife and I thought: ‘There are more people in there,’" Verite said. “But I was scared for myself and I wanted to help people. So I came outside and I was screaming because I knew where he was.”

Police have said that the first officers who arrived were shocked to find so many casualties.

Rudakubana was charged with three counts of murder in the 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 seriously wounded. Leanne Lucas, who led the class, and John Hayes, who worked in a business nearby and ran to help, were credited by police with trying to protect the children.

The stabbings fueled far-right activists to stoke anger at immigrants and Muslims after social media falsely identified the suspect — then unnamed — as an asylum seeker who had recently arrived in Britain by boat.

Within hours of a community vigil to mourn the Southport victims, an unruly mob attacked a mosque near the dance studio and tossed bricks and beer bottles at law enforcement officers and set fire to a police van.

Rioting spread across England and Northern Ireland that lasted a week. More than 1,200 people were arrested for the disorder and hundreds have been jailed.

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

He is due to appear by videolink Wednesday in Westminster Magistrates’ Court. His trial on murder charges was provisionally scheduled for January.

Dr. Renu Bindra of the U.K. Health Security Agency said Tuesday that “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.

The United States Chemical Warfare Service began studying ricin as a weapon during World War I. During World War II, Britain developed, but never used, a ricin bomb.

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.