The film clip released on Wednesday shows a young man pulling out a gun at the Rågsved station to the south of Stockholm.
"The assailant screamed at him to let him through, but he didn't, so he pulled a gun from his waistband," Peter Tapper at Stockholm police told the Aftonbladet newspaper.
The incident took place around 8.30pm on December 19th 2013 and was captured by CCTV cameras. The police have looked for the man since, but have no clue about his whereabouts nor of his identity.
"We want to know who he is and where he is," Tapper said.
The police said that the gun appeared to be loaded, which means the man is suspected of making aggravated illegal threats. As the man carried a gun, the police believe he could be involved in other crime.
"The offender may not think it's such a big deal to carry a gun," said Tapper.