it says colusa county sheriff's office, colusa, california, no street address and in the upper left-handyala case and then there are eight stamps on it. it was pretty light. it was way too much postage. >> reporter: because inside was just a single sheet of paper. an open letter to the cops. what did that letter say? >> reporter: basically it was claiming responsibility for the bombing. >> the letter full of misspellings and bad grammar had been written on a label maker then photo copied. it said a military trained contract killer had been hired to kill roberto over a mexico deal gone wrong and that it was ms 13 behind it. >> reporter: what the heck is ms 13? >> it's a violent el salvadorian criminal street gang. >> reporter: and that roberto was supposed to be a target of this group? >> the letter implied roberto had messed with a drug cartel and that ms 13 had been contracted. >> the author of the letter taunted the detectives writing the lab results would find military grade powder but no dna which was true so far. the point of the letter wrote its author was a warning. roberto's brot

also with us, michelle colusa from gilt group.t in, what you -- you parachute in, would you tell everybody at bnp paribas? >> from the outset, it looks like a cultural problem. they have been warned about this. they still had money laundering, and i cannot figure out why, so there is a compliance issue, and maybe a leadership problem. there is a cultural problem. >> how do you define air errort? you have to teach against, rather, at hbs. how do you manage a normal human condition? >> we try not to teach arrogance at hbs, but the truth is, people follow what they think senior management wants, and obviously there was a culture in this thisny that even though was the law, they felt that they did not need to follow it. i do not really understand from the outside wide. >> the idea of the government is saying it is not what bmp did, it was that they kept doing it, even when we told them maybe this was not the thing to do. >> it speaks to belligerence. i'm not sure that deciding to maintain a given when a years worth of profits will be