The 28-year-old from Staffordshire had been imprisoned in 2012 after plotting to bomb the London Stock Exchange.
The bodies of a 32-year-old man and a 23-year-old woman were discovered at a house in Burton-on-Trent on Wednesday.
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All four were killed in the blaze on 5 February.
Two adults and another child are being treated in hospital.
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One man has been treated for smoke inhalation.
It took fire crews several hours to tackle the blaze.
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Police footage also shows him standing up and taking selfies.