The man is suspected of serious blackmail and of planning to cause serious damage to property.
Throughout Friday a large area was closed off while police searched for more devices. Police confirmed that specific threats have been made against one of the oil companies based in the harbour.
“We are now investigating whether the threat can be linked to the explosive devices,” said police officer Peter Matilainen, who is leading the search, to TV4.
On Friday afternoon a special vehicle turned up to take the suspected bombs away.
“It’s a military vehicle which is otherwise used for munitions clearance,” said Björn Pihlblad, spokesman for Stockholm police.
He told news agency TT that the police are exploring alternative security measures and continuing to search the area. But he explained that the police would not be able to destroy the devices where they were found because of the high quantity of explosive gas stored in the harbour.
A 700 metre stretch of the dockside was cordoned off and a stretch of railway used by local commuter trains running from Södertälje Sud to Södertälje hamnstation was closed. Water traffic has also been stopped and police banned low-flying aircraft while the investigation continues.
None of the people who work in the harbour area were able to get to their jobs on Friday.
The three devices were found at the fuel company Aga on Thursday afternoon. They were described as “plastic tubes which were blocked up at one end and had blinking lights and cords at the other end”.
Aga evacuated its staff but on Friday the company’s press officer, Anders Andersson, said that there was no specific threat against the company.
“We have had information that the threat has no connection to Aga,” he told Dagens Nyheter. “Nevertheless, we have asked all our staff to be extra vigilant.”