Answer
Genomic tools could be used to identify the source of the infectious agent by looking at genomic sequences (show the geographic origin or connect with some source known to have a version of the agent with particular sequences). Further, the infectious agent could have it's genetic sequences compared to natural versions to see if any deliberate changes have been made to make the infectious agent more powerful or resistant, though all of these arguments would be based on probability and not give absolute certainty.
Work Step by Step
To get to this answer, consider how a lab-generated infectious agent might differ from its natural counterparts, in terms of virulence, or how it might be identified as coming from a particular place/laboratory using genomic data.