A large buyer and servicer of Alt A mortgages is under investigation by the Federal Trade Commission as part of an ongoing probe of the business practices of nonprime companies. The revelation came in securitization prospectus filed Dec. 30 by Bear Stearns, which revealed that its EMC Mortgage subsidiary, which acquires and services primarily non-conforming mortgages, had been contacted by the FTC. Bear said the agency had issued a “civil investigative demand” – basically…