CRM type software for managing cases/investigations

Hello all! Our company deals with investigations, and we want to identify an online platform/solution we can use to log and assign complex cases to team members. The cases themselves can be complex, and it would be necessary to add associated individuals, and for those individuals to be associated with allegations, against a series of dependent dropdown options. We'd also want to be able create lots of checkboxes and custom text fields for the cases. Can anyone suggest something that might be suitable? Many thanks in advance!