Rising up the ranks, Zelig sought control over the fragmented Eastman Gang in 1908, after "Kid Twist" (Max Zwerbach) was murdered by a rival.

[1][page needed] After Zelig was arrested in 1911 for robbing a brothel, Jack Sirocco and "Chick" Tricker attempted to gain leadership of the gang by refusing to bail out their boss.

[2] He was a known associate of Louis Pioggi, aka Louie the Lump, who had murdered Zelig's mentor, Kid Twist Zwerbach, four years earlier.

Becker told Jack Zelig and members of the Lenox Avenue Gang, specifically, Harry "Gyp the Blood" Horowitz, Jacob "Whitey Lewis" Seidenshner, Louis "Lefty Louie" Rosenberg, and Francesco "Dago Frank" Cirofisi, that he wanted Rosenthal "croaked".

In the aftermath, District Attorney Charles S. Whitman made no secret of his belief that the gangsters who killed him had committed the murder at Becker's behest.

[3] Davidson claimed he had shot Zelig over a $400 grudge, but it was popularly believed he had been killed to keep him from testifying against Charles Becker in the Rosenthal murder case involving the Lenox Avenue Gang.