All explosives should leave scorchmarks or cratering of some sort in a room that is similar to fire damage but can be analyzed by a forensicist to determine the type of explosive used.
Irregular and low-quality metal shrapnel? Pipe bomb.
Patterned and high-quality metal shrapnel? Frag grenade.
This would be even better once/if new explosives are added to the game, such as plastic explosives or shaped charges, to determine what happened after the fact.
