Orlando nightclub shooting: Inside the investigation

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The latest developments show that the FBI questioned Orlando nightclub shooter Omar Mateen a total of three times over past years, even putting him under surveillance for a period of time. Co-workers say he boasted about having terrorist connections. After an investigation, the FBI concluded there was no sign of actual terrorist connections. Mateen’s encounters with the FBI did not disqualify him from buying guns because he was never convicted of any crime. NBC’s justice correspondent Pete Williams has more on the investigation into the worst mass shooting in U.S. history.