IMO, torture should be a last resort, but I am unwilling to forbid it completely. If they think he is serious about it, and really does have relevant information, then I would torture and suffer whatever consequences the legal authorities might deem fit. Of course the situations were it might actually do some good are extremely rare.
How does one define torture?
Pulling fingernails? I think we'd all say yes.
Waterboarding? We do that to Navy Seals.
Punching a suspect over and over again?