Fan Interference on Pop-Up?

The batter hits a high fly foul ball near the stands behind first base. The first baseman drifts over towards the 3-foot high fence the separates the live-ball playing field from the stands.  The first baseman reaches into the stands but as the foul ball hits his glove, a fan of the offensive team purposely knocks the ball out of his glove. What does the umpire do now?
 
Does the call change if the foul pop fly is within live ball territory and the fan reaches into the field of play and knocks the ball out of the first baseman's glove?
 
Call
It is not spectator interference if a spectator hinders a fielder who has reached into dead ball territory to make a play on a batted ball (NF 8-3-3e and casebook 8.3.3m).
 
If a spectator reaches into live ball territory and interferes with a batted ball, then the ball is immediately dead and the umpire uses his judgement to impose penalties (NF 8-3-3e and casebook 8.3.3g).
 
In the first play below, Moises Alou reached into dead ball territory in an attempt to catch Luis Castillo's foul pop up. Although Steve Bartman interfered with Mr. Alou's attempt to catch the batted ball, since the ball was in dead ball territory, there is no penalty, except Mr. Bartman has been the witness protection program since 2003.
 
In the second play, Jeffrey Maier reached into live ball territory and interfered with Tony Tarasco's attempt to catch Derek Jeter's fly ball. This spectator interference and Mr. Jeter is out.