When eccentric socialite and art dealer William M.V. Kingsland died two years ago, he left an extensive collection of Pablo Picasso paintings and other works crammed into his one-bedroom apartment - but no will.

Kingsland apparently had no heirs to claim the floor-to-ceiling stacks of sketches, sculptures and paintings, so city officials hired two auction houses to go through and sell off the collection. During that process, two movers made off with two Picassos.

They were caught and sentenced to probation, and the works were returned. But the problems with the collection were only beginning.

Christie's auction house discovered some of the art had been reported stolen in the 1960s and '70s, and a gallery owner who bought a portrait by John Singleton Copley from Stair Galleries found it had been donated to Harvard University in 1943 and never sold.

Pablo Picasso,1971

FBI art crime agents now are trying to figure out just how much of the collection was ill-gotten and whether Kingsland, a secretive man who rarely invited guests to his home, was involved in stealing the works.

At least 20 pieces of art are believed to have been stolen, including a bust by Alberto Giacometti valued at about $1 million, FBI art crime agent Jim Wynne said Monday.

The Stair Galleries reported four stolen works in its half of the collection, the rest of which was sold. The FBI has posted photos of Christie's half of the collection on its website in the hope that the rightful owners will come forward and claim the works.

"Because of the overwhelming size of the collection," Wynne said, "we decided the best and most expeditious course of action was to publicize the artwork to the general public."

 The FBI says art theft is a "looming criminal enterprise" with losses running as high as $6 billion annually.

Kingsland's collection, which came mostly from Manhattan galleries, was considered to be diverse and interesting, but it wasn't necessarily a find of epic proportions. Still, the Picassos pinched by the movers were worth at least $60,000 total, and other Picassos in the collection were worth about $600,000.

After Kingsland's death, shady details emerged about him, too. He was born Melvyn Kohn and had relatives he hadn't spoken to in years - though his estate is still being handled by the city. But the art mystery will likely end after the collection is sorted.

"Whether he was a thief or a good-faith purchaser, we couldn't come to a conclusion on that," Wynne said. "All we know is he ended up with this stuff."

The proceeds from the auctions will go to a city public administrator's office, which handles the estates of people who die without wills or known relatives.