fruitful 復習

　米国ペンシルバニア州で、4人の20歳前後の男性が行方不明になった事件についてです。

Foul play suspected in disappearance of 4 young men in Pennsylvania

Authorities in Pennsylvania said they suspect foul play in the disappearance last week of four young men who may all know each other, and that leads in the investigation are “hot” as they comb the area near where they vanished.

Tom Meo, 21, of Plumstead, Mark Sturgis, 22, of Pennsburg, Deam Finocchiaro, 19, of Middletown, and Jimi Tar Patrick, 19, of Newtown Township were all reported missing last week, Bucks County District Attorney Matthew Weintraub said at a press conference on Monday.

When asked if foul play was suspected in the case, Weintraub said, "it sure would seem so," but declined to share further information.

“The leads are incredibly hot, they’re very fruitful. We’re making great progress, but there’s so much more work to do,” he said.

http://abcnews.go.com/US/foul-play-suspected-disappearance-young-men-pennsylvania/story?id=48543816

取り上げる表現は"fruitful"です。「フルーツ」と"ful"「たくさん」が合わさるとどのような意味になるのでしょうか。
　『ジーニアス英和辞典』第4版(大修館)で調べてみると、「実りの多い、有益な、良い結果を生む」などとありました。LDOCEでは、"producing good results"や"land that is fruitful produces a lot of crops"と表現されています。
　したがって今回の場合は、手がかり（lead）が事件の解決に有益であることを表しています。(Akim)