Norwegian police said Monday that they were working on several tips in their search for two Edvard Munch (search) masterpieces, including a version of "The Scream," (search) after a bold daytime theft from an Oslo museum in front of stunned visitors.

The paintings were stolen from Oslo's Munch Museum (search) on Sunday by masked, armed thieves, who pulled them from the walls as visitors and staff watched.

Inspector Ivar Stensrud, of the Oslo police, said all available personnel were being to used to search for the paintings stolen, which he described as national treasures.

The thieves fled with "The Scream" and another famous painting, "Madonna," loaded them into a getaway car and sped off. No one was hurt. According to the Norwegian news media, the paintings, worth tens of millions of dollars were not insured against theft.

Stensrud said that tips, photographs and videotapes, had been streaming in. Police located the getaway car and the paintings' frames within hours of the heist.

"There has been a good response, but not more tips that we can manage to check out," Stensrud told the Norwegian news agency NTB. He also said they were going through photographs and videotapes taken at the crime scene.

It's the second time in a decade that a version of the iconic painting has been stolen. Another version of "The Scream" — one of four Munch painted — was stolen from Oslo's National Gallery in February 1994, but recovered three months later.

Stensrud said police are taking a broad approach to the investigation, and have not yet focused on one motive.

The main theories speculated on in the Norwegian news media are that the painting were stolen for ransom, or as so-called trophy theft, or possibly because the theft was an order from a collector.

Charles Hill, a former Scotland Yard investigator who helped solve the "Scream" theft in 1994, said it was unlikely that the paintings were stolen for a collector or for sale because they are too well known.

Witnesses said the thieves — two or three of them — simply stormed in and yanked the paintings from the walls.

"The Scream," Munch's best-known painting, depicts an anguished figure possibly listening to a scream while holding his hands to his head. The Munch Museum had two versions of the painting, a private collector owns the third, and the fourth — stolen and recovered 10 years ago — is on display at Oslo's National Gallery.

The stolen "Madonna" was painted in 1893-1894, and depicts an eroticized madonna with a blood-red halo in a dark, swirling aura. Munch later produced woodcut lithographs with a similar depiction.

Munch, a Norwegian painter and graphic artist who worked in Germany as well as his home country, developed an emotionally charged style that was of great importance in the birth of the 20th century Expressionist movement.

He painted "The Scream" in 1893, and together with "Madonna" it was a part of his "Frieze of Life" series, in which sickness, death, anxiety, and love are central themes. He died in 1944 at the age of 81.