Answer:
Substances used to make the bomb
The area it was placed
Which people were in that area
How the bomb was set off
Step-by-step explanation:
Examining the residues left at the scene by the bomb could tell forensics what the bomb was made out of, and the police could investigate possible leads about people who purchased (or have access to) such materials.
The area should give clues because security cameras could be used to trace who was there that should not be. There would be a possible suspect.
If it is a public place, then we can see if there is anyone of importance (to the suspect) that was there at that time.
If a remote detonator was used to set off the bomb, then the suspect would have to be relatively close to the bomb.