and then it's mailed in. once it's mailed in, the inmate will cut up pieces of the picture and actually sell it. >> narcotics inside prison can be sold for almost 30 times their street price. an ounce of heroine that might cost $800 can be broken up and sold here for thousands. >> we hit the house. the guy was selling dope out of the house. so there was probably dope in that building. >> to crack down on the gangs' narcotic network, corcoran has formed a highly trained intelligence-gathering team called the investigative service unit. our cameras were allowed access to follow this unit, along with a local canine team, while they set out on a surprise contraband bust. searching inmate cells for drugs, weapons and gang paraphernalia. >> nobody else knows we're coming. the captains don't know, nobody knows we're coming. so this is going to be a complete surprise to staff and everybody. >> head of the isu, sergeant