Techniques for detecting suspicious data object access requests indicative of potential insider threats are described. A suspicious access detection module (SADM) determines, based on access data describing a access requests issued on behalf of multiple users, groups of the users having similar patterns of accesses to resource groups, a set of the resource groups accessed by each of the user groups, and ones of the user groups that are to be considered nearby others of the user groups based on having a threshold amount of resource group access similarities. The SADM causes an alert to be generated responsive to a determination that a subsequent access request is suspicious because it accesses a data object of a resource group that is not within the set of accessed resource groups of the issuing user's user group, and because the resource group is not within the sets of accessed resource groups of any nearby user groups.