(CNN) -- Swedish authorities who released a passenger taken into custody after a plane made an emergency landing are trying to find a caller who tipped off police that a man onboard had explosives -- an assertion that proved untrue.

The plane -- which had 273 people aboard and was flying from Canada to Pakistan -- landed Saturday morning after the phone call, authorities said.

The man, in his late 20s, was confronted by authorities in a "very nondramatic fashion" as all passengers filed off the plane and was cooperative, said Stockholm Police spokesman Kjell Lindgren.

"He said that he doesn't understand anything and that he has no idea what this is all about," Lindgren said. "He also said that he could not understand why he had been the subject of these accusations."

After several hours, the Swedish Prosecution Authority issued a statement saying, "The on-call prosecutor has decided not to arrest the man who has been held suspected of bringing explosives onto an airplane. The suspicions against this man are not strong enough to formally arrest him and he is therefore free to leave Sweden."

The plane was allowed to continue to Pakistan later Saturday.

Lindgren initially said the man was suspected of "preparation of aviation sabotage," though a search of the aircraft and the individuals yielded no evidence of explosives.

Pakistan International Airlines Flight 782 was heading from Toronto, Canada, to Karachi, Pakistan, when it landed because of "security reasons," said Sultan Hassan, an airline spokesman.

The plane landed at Arlanda airport in Stockholm, Sweden, at 7:30 a.m. (1:30 a.m. ET) Saturday after a woman calling from a pay phone in Canada tipped off police that a man on the plane had explosives, police spokesman Janne Hedlund said.

Canadian authorities contacted the plane while it was in Swedish airspace, Hedlund said.

The man is from Pakistan and has a Canadian passport, Hedlund said.

The investigation is still ongoing, but is now focused on the caller in Canada, Lindgren said.

CNN's Mila Sanina, Samson Desta and Catherine E. Shoichet contributed to this report.