The FBI is pursuing a new lead in the infamous D.B. Cooper case, and a new book on the 40-year-old unsolved hijacking is set to come out next week.

Geoffrey Gray will release his new book "Skyjack" on Aug. 9, which is based on the 1971 mysterious hijacking of a jetliner. Gray's new book is set to come just one week after the FBI revealed it had received a new lead into the case.

The FBI is looking into a promising new lead from a retired law enforcement official that a man who died 10 years ago in the Pacific Northwest is Cooper, the hijacker who parachuted out of the back of a passenger jet with $200,000.

Cooper was never found.

FBI agent Fred Gutt told the Seattle Times that the agency got a tip from a retired law enforcement official that the dead man could possibly be Cooper. Agents have requested the man's personal effects and are trying to find fingerprints or DNA to compare with items the hijacker left behind, the paper reported.

But Gray told NBC News that he doesn't think the prints found on the airplane can provide a good match.

"The problem with the print is just that there (are) just too many prints. And the prints that the FBI has been able to find aren't necessarily good ones," Gray said.

Gutt has said that the information the agency now has "hasn't produced inconsistent information, so in that regard it's still viable, credible and active."

Three years ago, the FBI found DNA evidence on the clip-on tie Cooper left behind on the plane before he jumped.

More than 1,000 leads have been checked since Cooper leaped out of the jetliner on Nov. 24, 1971, over the Pacific Northwest.

Gutt told the Seattle Times that the FBI tested an item from the dead man's belongings for fingerprints and it was inconclusive. However, agents are working with surviving family members to get other items for additional testing.

Watch the unsolved mystery here.