Dhaka, Nov. 30 -- A near-pristine copy of the first-ever Superman comic, discovered in an attic by three brothers cleaning out their late mother's San Francisco home, fetched a record-breaking $9.12 million at a Texas auction this month, setting a new high for comic book sales.

The brothers uncovered the comic, along with a handful of other rare pre-World War II issues, beneath layers of newspapers and dust. Their mother had once mentioned the collection's value, but the siblings had never seen it until preparing the house for sale, according to Lon Allen, vice president of comics at Heritage Auctions. Allen inspected the comic earlier this year and confirmed its exceptional condition.

Released in 1939 by Detective Comics Inc., Superman...