When deciding whether to interrogate someone solo or to do it in a team setting, I would take into account three types of factors. First, I would need to think about the apparent personality of the person being interrogated. Second, I would need to think about the characteristics of the people I had available to do the interrogation. I would try to match the resources I had with the challenge as I perceived it. Finally, I would need to look at the potential length of the interrogation process.
First, I would look at the person being interrogated. Does the person seem to have any obvious personality traits that might need to be worked with or around? Is the person particularly religious? What culture does the person come from?
Then I would look at the people I had available to me. Do I have someone who would be sure to get along with the person being interrogated? Do I have various people whose specialties (in terms of their technical knowledge) or whose mannerisms would mesh particularly well with the person being interviewed?
Finally, I would look at the duration of the process. If the interrogation seems like it will go on a long time, I would be more likely to assign a team so that they could be fresh by taking turns interrogating. This would put more pressure on the person being interrogated because that person would be much more tired than the interrogators.
Based on these sorts of questions, I would make my decision. I would decide if I needed to put together more than one person in a team or if I should assign one person.