Where did you see the house? Generally, when a bank lists a foreclosed home for sale, they hire a real estate agent to represent them and it will appear in the local Multiple Listing System. There you will find the name and telephone number of the listing agent. However, you should also know that any real estate agent can help you put an offer in on the home. My advice would be to find a good local agent to work with as a buyers' agent. Look for the SFR (Short Sale and Forelcosure Resource) designation and/or the CDPE (Certified Distressed Property Expert) designation.
Also, you need to be aware that there are services that merely print a list of homes that have been served with a notice of foreclosure or that have actually been foreclosed on. They look like for sale listings, but they are not and it can be confusing. These homes will only be available for purchase once the owners, whether that is the bank or the owner in default, lists them with a real estate professional.