Frainey was a private investigator hired by Locke to investigate his parents. He visited John at his workplace to tell him what he had found out about his mother and father.
He told Locke that he had lifted hairs from Emily Locke's car and had compared them to his DNA to confirm with "99%" accuracy that she was his biological mother. He also produced copies of her driver's license and her Santa Rosa admission record.
Concerning his father Anthony Cooper, he warned Locke that he'd "done this enough times to know this stuff isn't meant to be" and that "this probably won't have a happy ending". He was overall correct. ("Deus Ex Machina")