Story highlights Mohammed Rehman and Sana Ahmed Khan were arrested in May

Authorities found a stockpile of chemicals and bomb-making equipment

(CNN) A married couple plotting a massive suicide bombing to coincide with the 10th anniversary of the London transportation system attacks were convicted Tuesday of preparing for acts of terrorism, officials said.

Mohammed Rehman, 25, and his wife, Sana Ahmed Khan, 24, were arrested in May after authorities noticed extremist posts on Rehman's Twitter account, including one that appeared to ask for advice about what sites in London to bomb.

"Westfield shopping centre or London underground? Any advice would be appreciated greatly," said one tweet, which included a link to an al Qaeda statement on the July 7, 2005, terror attacks in London that left 52 people dead and as many as 300 wounded.

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Other tweets "included extremist rhetoric alongside images of homemade devices and instructional material" and authorities also found that Rehman conducted online research about ISIS, how to make explosives and the July 7 attackers, according to a statement from British counterterrorism police.

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After the pair were arrested, police searched Rehman's home and found a stockpile of chemicals and bomb-making materiel, the police statement said -- purchases apparently made online and financed by Khan, who took out loans and transferred money to her husband's account.

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