Both young sleuths felt sure there was a link between the two.

The correct answer is: detectives.

A detective is a person who investigates crimes. They are trained to gather evidence, interview witnesses, and solve crimes. In the context of the question, the two young sleuths are detectives who are investigating a crime. They are sure that there is a link between the two crimes they are investigating.

The other options are incorrect because they do not fit the context of the question. Travellers are people who travel from one place to another. Boys are young males. Convicts are people who have been found guilty of a crime and sentenced to prison.