Former FBI investigator Robert King Wittman has written a book about his career tracking down the world's top art thieves. Mei Jia reports on a world of gangsters, intrigue and very valuable artworks.

Former art crime investigator Robert King Wittman still remembers the time he retrieved the world's second largest crystal ball, which once belonged to Empress Dowager Cixi of the Qing Dynasty (1644-1911).

The crystal ball, weighing 22.5 kg, was found in a young woman's bedroom in New Jersey in the United States, one year after it was stolen from a Philadelphia museum.

"The once-gorgeous exhibit was there on a dresser with a baseball cap on it," Wittman says. "She used the cap to shield it from the sunlight in case it acted as a conduit to start a fire."

During his 20 years with the US Federal Bureau of Investigation, Wittman went undercover to mingle with gangsters and the mafia, and rescued stolen artworks and antiques worth more than $300 million in total.

The list of recovered artworks includes the Auguste Rodin sculpture that inspired the Impressionist movement, Pearl Buck's manuscripts of the Pulitzer-winning The Good Earth, the original manuscript of United States Bill of Rights and Rembrandt Harmenszoon van Rijn's small 1630 Self-Portrait valued at $36 million.

Wittman recounts the stories behind these recoveries in his memoir, Priceless: How I Went Undercover to Rescue the World's Stolen Treasures. The book is written in a readable, entertaining style to alert the public to the importance of preserving cultural heritage.

"Once you lose it, basically, it's gone. Then you lose your history. And if you don't know where you came from, you'll repeat the mistakes," the former agent says.

The book was praised in The Washington Post, which wrote: "Almost every case he recounts has enough intrigue and suspense for a Hollywood screenplay."

The book has been released in Chinese by Hangzhou-based MatrixBook.

Wittman chronologically retells 15 stories from his career, "like a true crime story, weaving in a bit of history", he says.

Wittman wrote most of the book from memory, checking court records, media files and other sources to verify the details.

Born in 1955 in Tokyo to a Japanese mother and American father, Wittman's family moved to the US in 1958. Because of a lack of knowledge about Asian countries at that time, his mother was a victim of racial prejudice.