Once Otto was hired as the getaway driver, Krusty knew that if this heist was to be pulled off, they would need muscle as well.
Krusty suggested to head of his gang, Homer, that they enlist two of his personal drug runners, Lenny and Carl, otherwise known as Krusty's Kocaine Cowboys. Both hustlers had been distributing Krusty's Koke through the Krusty Burger front for years now, and had help Krusty bring in hundreds of thousands from off shore accounts over the months.
Before they ran Krusty's drug distribution Lenny and Carl had sold and distributed drugs in Russia for years prior. Krusty had been on tour in Europe, and was introduced to both off-stage. He quickly realized their potential and set both of them up in Springfield, both with luxurious homes and rides.
However, not much was known about the two. Rumors of Lenny being in the Russian mafia flew around Springfield once he settled, and his tattoo's didn't help. Carl didn't speak much, but everyone knew that when he did, you had better shut your goddamn mouth and listen.
The two kept a low profile, only making moves when they were required. This is why Krusty hired them. He trusted both, and for a reason, one Homer wouldn't be able to understand.
Because if this heist was to truly be accomplished, it would require Homer's son Bart.