The Liverpool bomber began making "relevant purchases" for his attack in April, counter-terror police have said.
Emad Al Swealmeen died in an explosion outside Liverpool Women's Hospital in a taxi shortly before 11am on Remembrance Sunday.
Assistant Chief Constable Russ Jackson, head of Counter Terrorism Policing North West, said a post-mortem had now been completed and determined the cause of death as "injuries sustained from the fire and explosion".
"A complex picture is emerging over the purchases of the component parts of the device, we know that Al Swealmeen rented the property from April this year, and we believe relevant purchases have been made at least since that time," said a statement.
"We have now traced a next of kin for Al Swealmeen who has informed us that he was born in Iraq.
"Our enquiries have found that Al Swealmeen has had episodes of mental illness, this will form part of the investigation and will take some time to fully understand."
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