“It’s a breakthrough,” Stockholm police Commissioner Lef Jennekvist told reporters late Tuesday evening. But he also cautioned against jumping to conclusions after the arrest saying, “this is the beginning of a long and difficult investigation.”

Jennekvist said the man resembled the person filmed by store security cameras at the time of Lindh’s death. Lindh, one of Sweden’s most popular politicians and often tipped as a future prime minister, was brutally stabbed by a man on September 10 while shopping without body guards.

Lindh was a leading member of the pro-euro campaign to get Sweden to join the euro zone, but police have said there is so far no evidence of a political motive for the killing. Despite an upsurge in sympathy for Lindh’s pro-euro views, Swedes chose to keep the krona on Sunday by a large margin.

Plain-clothes police arrested the unarmed suspect, who has not yet been named, at 9:07 p.m. local time outside a pub-restaurant near Sweden's national football stadium Råsunda in a north Stockholm suburb after other patrons had recognized him.

Man reportedly unstable

According to the Swedish TT news agency, the suspect was a 35-year-old man with 18 previous convictions for crimes such as fraud and theft as well as violence and threats involving knives. A psychiatric examination in 2002 linked to one of these offences found the man was not mentally ill, TT said.

Under Swedish law, criminals declared mentally ill cannot be sentenced to jail but must undergo psychiatric treatment instead. Doctors have said the man has a narcissistic personality, and he has reportedly told a court he abused cocaine and alcohol.

“We will question the man who has been brought in, then we will let medical and legal experts examine him,” said Jennekvist.

The man has not yet been charged, as the authorities continued with tests to compare the man’s DNA with samples left on the murder weapon and a baseball cap left at the scene. Under immense pressure to make progress in the investigation, the Swedish police have called in help from British and German forensic experts.

The desire of most Swedes to see Lindh’s murderer brought to justice has been compounded by the fact that the 1986 assassination of Swedish Prime Minister Olof Palme remains unsolved. Like Lindh, Palme did not have any bodyguards with him when he was shot in Stockholm.