After creating the event I save the eventIdentifier in an array:

[eventStore saveEvent:event span:EKSpanThisEvent error:&err]; 
   NSString* str = [[NSString alloc] initWithFormat:@"%@", event.eventIdentifier];
[arrayofCalIDs addObject:str];

To delete the events:

EKEventStore* store = [[[EKEventStore alloc] init] autorelease];
   EKEvent* event2 = [store eventWithIdentifier:[arrayofCalIDs objectAtIndex:i]];
if (event2 != nil) {  
  NSError* error = nil;
  [store removeEvent:event2 span:EKSpanThisEvent error:&error];
} 
[myPath release];