when babcock is being investigated, grant writes a letter to babcock's wife saying, i have full faith in your husband's integrity. i've had the most intimate and confidential relations with her husband for 14 years. he says i can't believe that he's not a trustworthy person that i imagine. guess what? he was. he was kind of like chief of staff. he had the desk right outside grants office. he would review incoming and outgoing mail. grant fired him or reassigned him. he became inspector of lighthouses on the florida coast. [laughter] >> after he leaves office, grant goes on a trip around the world with his wife for 2 and a half years. how was he received on this trip? ron: it is a post-presidency unlike any other. during that time, he meets with virtually every head of state in the world. queen victoria. who sees him at windsor castle. he sees the prince of bismarck receives him in berlin. , the pope at the vatican. czar alexander ii in st. petersburg. then he goes to the far east and the crowds are immense. like 250,000 people at a time would turn out. the emperor of japan would never

a name and face detective babcock knew quite well from an encounter in 1999, when babcock was workingice unit in albuquerque. >> the vice unit was watching a particular prostitute. see a vehicle pick this girl up. drive to a remote location. we approached the vehicle, open the door, the first words out of this girl's mouth, who's a known prostitute, was that he was trying to kill her. >> and the man in the car was? >> lorenzo montoya. >> reporter: lorenzo montoya, a short, powerfully built man in his 30s who was known to have an equally short temper and a taste for prostitutes. babcock says he saw marks on the woman's throat and that she told him montoya looked like he was enjoying it. >> did you believe her story? >> yes. >> so lorenzo was arrested for charges beyond just patronizing a prostitute. >> yes, he was. >> reporter: that felony assault charge against lorenzo montoya went nowhere because the victim later refused to testify. but it was what had happened next that really focused the detectives' attention. in 2006, years after being caught in the act of choking one prostitute,