Noble Cause Corruption

Keeping in mind noble cause corruption and the ethical issues in regards to it consider the following scenario. You are a detective and are interrogating a suspect in a robbery case.  You tell the suspect that several witnesses will be viewing him in a lineup and he will be picked out, so it would be better for him if he comes clean. The suspect does not make a statement and the lineups proceed, the first witness fails to pick the suspect out, and the second picks him but is not 100% sure and states such to the detective. After two failed identifications the detective goes back into the interrogation room with the suspect and tells him that both witnesses picked him out. This prompts the suspect to make a complete confession. Was this confession legally obtained? What are the ethics relative to this confession? Is this a case of noble cause corruption? Will this confession hold up in court?  .