The most effective way to get information from someone that is being interrogated is not going to be through sheer might, although exerting intense psychological and physical pressure against someone is very likely to get some sort of response, but not necessarily 100% actionable information. In addition, in all fairness, whatever coercive techniques are used to extract intelligence, means, that if the shoe was on the other foot, they would have a somewhat justified case to utilize the very same techniques upon you. In actuality, the very best way to look upon interrogation is as a process in which we avoid the temptation to use "by any means necessary" and instead take advantage of our skill-sets, knowledge, and superior ability to correlate and to analyze information obtained.
Anytime that a conversation is taking place between individuals, there is a produced a slew of information, such as the actual verbal intercourse, body language, tone, and everything in-between. Therefore, the department that takes copious notes, video records, watches, analyzes, adjusts to information derived or obtained, and at the same time is able to build a rapport with the person being interrogated is on a pathway to developing a successful negotiation. The one big difference between truth and lying is that truth at its very core has but one story, and that story does not change; whereas lying builds upon a false foundation, that can easily collapse upon itself, so asking questions and then correlating and connecting the answers to those questions has an immense validity. Another important thing is that the more a person talks, the more information that they will give up, inadvertently or not, so it is important to get a conversation going, and that conversation can begin with very banal things, that shouldn't be seen as threatening at all to one that is being interrogated.
Also, too, the more civil and respectful that you are to the person that is being interrogated, the better the chances are that after a period of consideration, a conversation can be induced. While fear and pain, can often quickly get results, the problem with those results, besides the moral and legal issues, is that you may only get the tip of the iceberg, or you may get a mixture of real information along with misinformation that appears valid, as well as you may just hear what you want to hear, because you aren't actually engaging in a conversation. An interrogation should be a negotiation, to which, a fair trade is exchanged, as there has to be something in it for the person being interrogated, even something as basic as respect, or you will not be able to make the connection that you wish to achieve.
Then too there must be the fundamental realization that not every interrogation is going to work out effectively, that is part and parcel of the business; you're obligation is solely to conduct your business in a professional and at a proficient level. Also, it is of immense importance not to lose sight of the fact that despite the apparent exigencies of the situation, often times that urgency is not in actuality as grave as it may appear, in point of fact, sometimes through bureaucratic inexactitude and inefficiencies, your hard work will be all for naught. Additionally, and of utmost relevance, it is no credit to yourself or to this nation, to undercut the basic moral principles that this country aspires to for sadistic short-term satisfaction.