In Hollywood movies, heists usually feature criminals who plan meticulously and use high-tech equipment to avoid detection. But the thieves who snatched seven paintings by Picasso, Matisse and Monet worth millions from a gallery in Rotterdam appear to have taken a less glamorous approach, relying mostly on speed and brute force.

In other words, the theft from the Kunsthal exhibition on avant-garde art was more "smash and grab" than "Ocean's 11."

Dutch police said Wednesday they had no suspects in the case, the largest art heist in the country for more than a decade, though an appeal to witnesses had produced more than a dozen tips for investigators to follow up.

As questions arose about security at the museum, its director, Emily Ansenk, rejected criticism of the facility's safeguards. Speaking at a news conference Tuesday evening, she defended Kunsthal's security as "state of the art" and noted that insurance companies had agreed to insure it.

And yet the thieves got away. The paintings they took are estimated to be worth roughly $100 million if sold at auction.

Experts said the structure and location of the museum, which was designed by renowned Dutch architect Rem Koolhaas, may have attracted criminals.

"Speaking as a museum-goer, it's fantastic," museum security expert Ton Cremers said. "Speaking as a security expert, it's a total nightmare."

The gallery is located along a large road that leads to a roundabout, less than a mile away, connecting highways heading in three directions. The display space where the paintings once hung is a large square area, at ground level, visible from outside through glass walls.

Though police and the museum have declined to discuss aspects of the heist that might help thieves, the main details of what happened are clear.

The break-in occurred at around 3 a.m. Tuesday, police say, after someone triggered an alarm.

Investigators have focused on an emergency exit behind the building. The exit connects directly to the main exhibition hall, with paintings hung just a few yards away. Tire tracks can still be seen in the grass behind the building leading away from the exit. Police on Tuesday dusted the exit for fingerprints and took samples of the tire prints.

The paintings were yanked from the walls, leaving only white spaces and broken hanging wires dangling behind.

Officers were on the scene within five minutes of the alarm being triggered, according to museum director Ansenk, but the thieves were already gone.

Police spokesman Henk van der Velde said Wednesday that 25 officers have been assigned to the case, but the getaway car has not been found and there are no suspects. Agents were reviewing videotape from museum cameras.

It is unknown what will happen to the paintings if the thieves are not caught.

The thieves may "wake up and realize they can't sell the paintings easily" now that museums around the world have been alerted to their theft, said Chris Marinello, of the Art Loss Register.

But the thieves may also sell them on the black market for a fraction of their true value, or try to extract money from insurers in exchange for returning them.

Anthony Roman, a New York-based security analyst, said the Kunsthal's level of defenses appeared so basic as to be "astounding," given the value of the art it was housing. He said an alarm system alone would never be enough to stop criminals.

Thieves "learn the distance the police have to travel," he said. "They understand the mechanism and the amount of time between when the alarm goes off and the time of a physical presence of law enforcement."

Security expert Cremers said the museum was not at fault for relying on cameras and motion detectors, rather than human guards. Having guards on site is costly, and they would be instructed not to confront robbers during a break-in anyway.

"The only thing they can do is call police," he said.

Cremers said the museum should have looked at ways to slow potential thieves down. That might have prevented them from attempting to break in in the first place, or at least limited the size of their haul.

He said the paintings should have been hung inside behind a second makeshift wall with doors, creating a "box within a box" in the gallery. In addition, the museum could have set up a barrier or fence preventing cars from being able to drive up right to the emergency doors.

"I'm sure they'll be looking at that now," he said.

Later Wednesday, museum spokeswoman Mariette Maaskant confirmed that the museum was installing stone planter boxes big enough to block cars "as an extra security measure."


AP reporter Lori Hinnant contributed to this story from Paris.