Sasori of the Red Sands' pawn controlled by Latent Brain Manipulation Sand seemed to be named Yura, if Wu Yu remembered correctly.
At the beginning of Shippuden, it was only because Yura had already infiltrated Sunagakure's upper ranks that he could cooperate from within, throwing the doors wide open for the artistic duo of Deidara and Sasori. They slipped into Sunagakure as easily as crossing a road in the morning and captured Gaara, the Fifth Kazekage at the time.
Wu Yu did not know how far Yura had climbed by now, but Gaara was not the Kazekage either. Simply passing along the time and route of Gaara's mission probably would not be difficult.
With Sasori and Deidara's abilities, intercepting and killing an ordinary four-man Sunagakure squad in the wilderness could not have been easier.
Why was Wu Yu so certain the artistic duo had done it? Naturally, it was information provided by the Otsutsuki Third Prince, Black Zetsu.
Deidara and Sasori had taken Gaara away without leaving a single survivor. It was only after Sunagakure noticed something was wrong a day or two later that they sent people out to search. They found the bodies of Gaara's other three teammates, buried beneath the sand and dust, and concluded that something had happened to Gaara.
Acting Kazekage Baki dispatched several search-and-rescue teams while decisively requesting aid from Konoha despite the elders' objections.
Tsunade specifically appointed Kakashi Hatake to lead the new Team Seven to Sunagakure in the Wind Country. Black Zetsu detected the Nine-Tails' Chakra, then conveniently passed the information to Kakuzu and his companion, who happened to be wandering around an underground bounty exchange in the Fire Country.
Every Akatsuki member was an S-rank rogue ninja with strength comparable to a village's Kage. Each was proud as could be—who would