And Jack Riley is acting director of the Rand Corporation's Center on Quality Policing.

NPR: Shooting Strains Police-Community Ties in NYC

But Jack Riley says that Guzman, whose nickname El Chapo means "shorty" in Spanish, is more ruthless than the legendary gangster.

BBC: Chicago names Joaquin Guzman public enemy No. 1

Jack Riley, the author, says he was surprised by their willingness to talk, sometimes with no more inducement than a chocolate bar at the end of the interview.

ECONOMIST: Drug abuse