After a bomb explodes, the area is combed for physical evidence.
A trained investigator can spot which pieces of debris are important.
In the case of the abortion clinic bombers, whose case was described in our NOVA program, "Bombing of America," various pieces of evidence were recovered, which eventually led to the arrest of three suspects. In our television program, we discuss how the
gas canister and
from a molotov cocktail helped investigators track down the criminals.