Glock pistols do not have a hammer, they are striker fired and cannot be cocked without racking the slide, therefore the "click-click" sound heard twice in the same scene is not possible. It's not just this episode, it appears constantly throughout the whole series.
Harold Cooper states that the terrorists have "a metric ton of C4".
When the van containing the terrorist's bomb is opened, there is no C4, but a timer and 20 barrels of accellerant, ammonium nitrate and fuel oil.
Where'd the C4 go to?
The prop "detonator" found in the front seat of the stolen truck is the same prop "detonator" Gina Zanetakos uses to blow up the SUV used in the robbery in Episode 13 "Alistair Pitt."
After an extended confrontation and conversation with Gina, Tom racks the slide of his Glock pistol (charging the weapon). Since a Glock is a hunk of useless metal and polymer before the slide is racked, it is inconceivable that Tom would not have done that much earlier, before Gina entered the room.