container that looks like this. >> the vast majority of fentanyl is produced in china. it comes into the u.s. two ways. you know, it comes into next, where it's either pressed into pill form or combined with heroin. the other way it comes in, american consumers buying it direct, oftentimes from vendors out of china. >> then i want gets mailed in? >> u.s. mail, which is the most common. a very small quantity of fentanyl is very hard to detect in the masses of letters that come into the u.s. every day. >> how effective is a wall at preventing drugs from getting into the united states? >> in terms of hard narcotics, no, i don't know that we get an immediately safer over hard narcotics. as of right now, the vast majority of hard narcotics come in through the ports of entry, in deep concealment, or come in through, you know, the mail order express consignments. >> ports of entry, right? i mean, as in, not in that unwalled -- ports of entry are