The discovery of a collection of the writings of Malcolm X could throw new light on the philosophy of the murdered black leader. But plans to sell the documents have led to a dispute between his family and a San Francisco auction house, and have reopened the debate about the ownership of intellectual property.

The archive - comprising hundreds of pages of diaries, drafts of speeches, letters and photographs - was reportedly found in a self-storage centre and is to be sold on March 20 by Butterfields, the auction house owned by the internet giant eBay. Estimates suggest the collection could fetch as much as $500,000 (£310,000).

Academics believe the collection could force a rethink of Malcolm X's philosophy and a re-evaluation of his work. Abdul Al kalimat, the director of Africana studies at Toledo University in Ohio, told the New York Times: "This collection is far and above the mother lode. This is likely to force the rewriting of all the books, at least on the whole question of what happened during the last year of his life."

Life's works

After becoming a Black Muslim in prison, Malcolm X became a leading spokesman for black rights before forming his own Organisation for Afro-American Unity. He was shot dead in New York in February 1965 at the age of 39.

The items for sale include four notebooks in which he describes two visits to Africa in the year before his death, and writings spanning more than 20 years. His personal copy of the Koran, estimated at $30,000, is also for sale.

What remains a mystery is how the collection was discovered. The owner has not been identified but Butterfields confirmed that it was acquired through an auction at a facility that allows customers to rent storage space. The auction house said if the seller had not spotted the material it might have ended up on a rubbish tip.

But Malcolm X's family, which has authenticated the works, is unhappy that the collection is up for sale and could be split up. Joseph Fleming, the lawyer who represents some of Malcolm X's six daughters and the estate of his late wife, Betty Shabazz, said the daughters were unhappy to see the legacy up for auction.

Mr Fleming is seeking an injunction to halt the sale. In 1999, the family successfully stopped an attempt by the auction house to sell a bloodstained address book said to have been found on Malcolm X's body when he was shot.

The dispute highlights the debate about who owns the writings of the dead. The growth in the market for archives of famous writers or politicians has made them big business, and original works can fetch millions. There is concern in the academic community that work that could be held and maintained by a university and made available to researchers may be lost as individuals acquire them for private collections.

Butterfields, which is selling items connected with Raymond Chandler, Scott Fitzgerald and Zane Grey at the same auction at its offices in San Francisco and on eBay, is now considering selling the Malcolm X items as one lot rather than as the 19 separate lots currently advertised.

One likely bidder is the Schomburg Centre for Research in Black Culture, a division of the New York public library. The centre's director, Howard Dodson, said it would "seek to acquire the collection by any means necessary", echoing one of the phrases for which Malcolm X was famous.