A Syrian refugee arrested on suspicion of planning a major attack in Berlin reportedly spoke to a member of Islamic State in Syria by telephone about a possible target a day before police discovered explosives in his apartment.
Jaber Albakr was detained on Monday, two days after police discovered about 1.5 kg of explosives in his apartment.
He was found dead in prison on Wednesday. Authorities said he had died from suicide.
Germany's Welt am Sonntag (WamS) on Saturday cited investigation sources as saying US intelligence had provided a tip-off on Albakr after tapping several phone calls between him and an Islamic State member in Syria. During the calls, 22-year-old Albakr spoke about his attack plans, the newspaper said.
In a call on October 7, Albakr told his contact that 2 kg of explosives were ready and he named a possible target, saying a "big airport in Berlin" was "better than trains", WamS reported.
In July, the militant group claimed responsibility for two attacks in the German state of Bavaria - one on a train near Wuerzburg and the other at a music festival in Ansbach that wounded 20 people.
Federal prosecutors investigating the case assumed that Albakr wanted to make a vest packed with explosives for an attack.
Albakr arrived in Germany in February 2015 during a migrant influx into the country and was granted temporary asylum four months later.
The man who rented the flat in the eastern city of Chemnitz in which Albakr last lived - a 33-year-old Syrian who WamS named as Khalil A. - is in custody and is being investigated on suspicion of helping Albakr, the newspaper said.
Separately, Berliner Morgenpost newspaper and regional broadcaster rbb cited federal security sources as saying Albakr spent a night in Berlin in the second half of September and met a contact there.
During that time, he visited one of the city's two airports, they added, without saying which one.
The federal prosecutor's office declined to comment on the reports when contacted by Reuters.