Answer:
The agent probably knew about the murderer, because the accused only bought a ticket to return from the trip.
Explanation:
When the friend bought the travel tickets, he did not buy two tickets back, but only one, that is, he knew that his friend would not return, although he did buy two one-way tickets. Thus, this individual becomes the main suspect in the murder, since only the two friends were on the trip and it is necessary to investigate all the possibilities of his friend's death.
In this case, the police contacted the travel agent who passed all the ticket purchase information between the two friends.
