Like most terror operations involving suicide bombers there are scouts who survey and locate targets and target areas first. Sometimes the scouts act as handlers on the side, holding a remote to detonate the bomb if the bomber changes their mind or loses nerve.
Right now the London terror trials reveal the miscreants who assisted the bombers.
From The Daily Mail:
These are the three men accused of helping the 7 July bombers to identify possible targets in London.
The three were due to stand trial today – the first prosecution in connection with the atrocity – on charges of conspiring with the four suicide bombers to cause explosions.
As a jury for their trial was sworn in today, a judge lifted an order banning publication of drawings or photographs of the accused men.
Waheed Ali, 24, Sadeer Saleem, 27, and Mohammed Shakil, 31, all deny conspiring to cause explosions.