“We have received information from the secret services that he initially wanted to target trains in Germany before finally deciding on one of Berlin's airports,” Hans-Georg Maassen told German public TV channel ARD.
While some German media outlets over the weekend suggested the suspect, Jaber Albakr, 22, had such a target in mind, this was the first official confirmation.
The decision to arrest the suspect was taken on Friday after he bought hot-melt glue.
“We thought this was the last chemical product he needed to make a bomb,” said Maassen.
Albakr had narrowly slipped through the police net Saturday when commandos raided his apartment and found 1.5 kilos (over 3 pounds) of TATP, the homemade explosive used by jihadists in the Paris and Brussels attacks.
The explosives were “almost ready, or even ready for use”, said Jörg Michaelis, chief investigator in the eastern state of Saxony, adding that the suspect was apparently preparing a “bomb, possibly in the form of a suicide vest”.
'He tried to bribe us'
After a two-day manhunt, police finally got their man with the help of three of Albakr's fellow Syrians in the eastern city of Leipzig.
One of them walked into a police station with a photo of Albakr on his mobile phone and told officers that “his flatmates had overpowered Albakr and tied him up, and that we should come to his apartment,” Michaelis told reporters.
The Syrians had earlier been approached by Albakr at Leipzig railway station and asked for shelter. They took him home, only to find out in a police alert that he was the bomb plot suspect on the run.
He said Albakr offered them €1,000 and $200 to allow him to go free.
“He tried to bribe us, but we told him he could give us as much money as he wanted, we wouldn't free him,” one of the men told RTL television, speaking with his back to the camera and identified only as Mohamed A., for fear of reprisals.
“Then we got an electrical cord and tied him up until the police got there,” he said, providing RTL with a smartphone picture of their detainee.
“I was furious with him, I couldn't accept something like this – especially here in Germany, the country that opened its doors to us.”
Chancellor Angela Merkel on Monday expressed her gratitude, saying the Syrians had “made a decisive contribution” to the arrest.
Police had first closed in on Albakr on Saturday in the eastern city of Chemnitz, about 85 kilometres (50 miles) south of Leipzig, acting on information from the domestic security service.
But he narrowly evaded police and ran off carrying a backpack, shortly before police found the explosives, sparking a nationwide manhunt.
Preliminary investigations suggest that Albakr was probably linked to the terror group Isis, police said.
Interior Minister Thomas de Maiziere said the plot “resembles what we know of the preparations for the attacks in Paris and Brussels”.
Albakr's Syrian flatmate in Chemnitz, named only as Khalil A., was formally taken into custody Sunday, a day after being detained, as a suspected co-conspirator.
Albakr entered Germany on February 18th 2015 and two weeks later filed a request for asylum, which was granted in June that year.