Investigators probing who may have provided WikiLeaks with classified information about the Central Intelligence Agency’s purported computer-hacking techniques are zeroing in on a small number of contractors who have worked for the agency and may have been disgruntled over recent job losses, according to people familiar with the investigation.

Authorities on Thursday questioned a handful of contractors working in at least two locations in the Virginia suburbs of Washington, D.C., these people said. Law-enforcement officials...