Neither.
Bomber gets on bus, waves ID (easy enough to get one, legit or fake), gets in, blows up. How did checking ID help?
The problem, repeatedly explained and repeatedly ignored, is that the only thing the ID check does in this scenario is ensure that someone has an ID. Unless the ID is checked as being FOR THE FACILITY, or CHECKED AGAINST A TO-ENTER LIST, checking an ID only serves to show that someone gave this person an ID.
If someone is that determined to cause that much trouble, they'll get something that will sufficiently pass as an ID.
ID checker notices something suspicious, document seems not quite right, there IS no document, subject seems nervous, dress not appropriate for time/place/weather, ID reques and inspection allows close-up face to face eye contact, subject panics, etc., etc., etc. No ID check, 100% chance none of the above will happen.
If said bomber 'waved' ID, then it wasn't checked. Is this what you meant? Seems you are slanting your example to suit an agenda. How about bomber doesn;t 'wave' ID, bomber has ID checked, is asked for 2nd ID, is questioned, etc.