The brother of Jaber Albakr said that a Berlin imam had radicalized the 22-year-old after he fled to Germany from Syria, Spiegel reported on Friday.
Before Albakr fled from Syria in 2014 and arrived in Germany in early 2015, he was not political, his brother said.
“My brother was radicalized in Germany,” Alaa Albakr told Spiegel over the phone from Syria.
Alaa said his brother had seen horrible videos of Syria posted online, and the Berlin imam had brain-washed him, encouraging him to go back to Syria to fight. The brother could not say which preacher the 22-year-old had spoken with.
In September 2015, Albakr went from Germany through Turkey to Raqqa - the de facto capital of Isis - and joined the terror group. After he told his family that he had allied himself with the group, they cut off contact with him.
Public broadcaster MDR has reported that Albakr went back to Syria from Germany twice.
Still, Alaa Albakr said he could not believe that his brother could have planned an attack.
“I raised my brother. We would never commit an attack. That is a lie,” the older brother said.
Police arrested the younger Albakr on Monday in Leipzig after a weekend-long manhunt in the eastern state of Saxony, having found explosives in his Chemnitz flat.
Intelligence authorities have said that they received information Albakr was initially planning to target trains in Germany, before deciding instead to attack a Berlin airport - and the attack may have only been days away.
He was captured with the help of three other Syrian refugees, who had initially given him a place to stay before realizing he was a wanted terror suspect and alerting police.
The 22-year-old was found dead in his cell on Wednesday in an apparent suicide, prompting criticism of authorities for not watching him closely.
‘Mistakes made’ by authorities
Saxon officials have been under pressure since the manhunt for Albakr was initially announced last weekend, first facing criticism for letting him slip away when they raided his flat on Saturday, and most recently for the fact that he hung himself in his cell while in custody.
His lawyer Alexander Hübner told Focus news weekly that the jail was aware that he was a suicide risk and angrily called the death a "judicial scandal".
"He had already smashed lamps and manipulated power points" after entering a hunger strike shortly after his arrest, agreeing only to drink a glass of water, Hübner said.
On Friday Saxony’s Minister President Stanislaw Tillich admitted that officials had made mistakes before Albakr’s suicide.
“The handling of the terrorism prisoner was not performed to the extent that it should have been,” Tillich told reporters. “The suicide should in any case have been prevented.”
He also said he was open to an independent investigation into the suicide, though he dismissed the notion of replacing his justice minister.
The day after the suicide, prison director Rolf Jacob said a psychologist had determined Albakr did not pose an “acute suicide risk”.
But while Tillich on Friday acknowledged that “one can always do things better” and “learn from mistakes”, he said that overall it had not been a government failure.
Several German MPs as well as Interior Minister Thomas de Maizière have called for a rigorous enquiry into the suicide.
Help from US intelligence
Die Welt reported on Friday that a US intelligence agency had tipped off German intelligence about Albakr.
The newspaper reports that American agents had listened in on several phone conversations made by Albakr, including with suspected Isis contacts in Syria. He also spoke about producing explosives and of his attack plans.
“Two kilos are ready,” he reportedly told his Isis contact, probably referring to the 1.5 kilograms of TATP found in his apartment later by police.
He also said that a “big Berlin airport” would be “better than trains”. This call, according to die Welt, was the deciding factor in ordering the police raid on Saturday.
Albakr’s flatmate is currently under investigation for whether he was assisting in the bomb plot.