GWEN IFILL: In 16 states, marijuana use is legal for medical purposes, but authorities say state laws do not protect growers from federal prosecution.
Special correspondent Michael Montgomery of KQED San Francisco looks at how that conflict is playing out in one California community.
His story is part of an ongoing investigation by the Center For Investigative Reporting, "Frontline," and KQED.
MICHAEL MONTGOMERY, KQED San Francisco: Matthew Cohen cultivates medicinal marijuana on a 10-acre farm set amid rolling vineyards in Northern California. And for the past year, he's been operating legally, at least in the eyes of local law enforcement. His marijuana plants are protected by these tags.
MATTHEW COHEN, marijuana grower: That says Mendocino County Sheriff on it. It is upside-down, though.
MICHAEL MONTGOMERY: This program is unique in California and has allowed Cohen's nonprofit cooperative to expand around the state.
MATTHEW COHEN: We're about 1,700 members now.
MICHAEL MONTGOMERY: A county ordinance allows Cohen to legally grow up to 99 plants, provided he submits to inspections by sheriff's deputies and complies with state law. It's enough marijuana to keep his co-op members supplied for many months.
MATTHEW COHEN: We were just getting ready to start harvesting. We figured that we were compliant with state law and compliant with local regulations, and that that's not what the federal government was interested in.
MICHAEL MONTGOMERY: But Cohen was wrong. On Oct. 13, heavily armed federal agents stormed his compound.
MATTHEW COHEN: Our dog started barking. And then I looked out the window and saw four or five, you know, federal agent vehicles, you could tell, with the blacked-out windows and the blacked-out rims, come cruising in here. Everybody hopped out of the car very quickly. I told my wife, we're being raided.
They said, open up. Federal agents. We have a warrant. And I said, I'm opening the door right now. And I opened the door to -- you know, they had the battering ram ready to go through the door. And they grabbed me, slammed me up against the wall here cuffed me.
MICHAEL MONTGOMERY: As the agents searched other buildings on the property, Cohen's state-of-the-art security system recorded their moves.
MATTHEW COHEN: There's a machine gun right there.
MICHAEL MONTGOMERY: Under the Controlled Substances Act, marijuana remains illegal in the eyes of the federal government, and drug agents are stepping up raids across the state to curtail California's pot industry.
MATTHEW COHEN: You can see they tore through all our camping stuff. And these were just -- this is recycling that they went through.
MICHAEL MONTGOMERY: Before the agents discovered most of Cohen's surveillance gear, cameras caught them searching through his business files. Meticulous record-keeping is required by county law. But there's a twist. The same documents that allow Cohen to operate legally in Mendocino can be used against him as evidence in a federal criminal prosecution.
It was only after the DEA raid was under way that Sheriff Tom Allman learned that one of the farmers in his inspection program was the target.
TOM ALLMAN, Mendocino County, Calif., sheriff: That afternoon, after I assumed that everything had cleared, I called Matt Cohen. I asked him if -- how he was treated. And he said he was treated fair. He said he wasn't arrested. And he said that they cut down marijuana plants, 99. And I believe that's what their records show also.
I assured him that, in my opinion, as far as local and state laws were concerned, he was abiding by those laws.
MICHAEL MONTGOMERY: Days before the raid on Cohen's farm, California's four U.S. attorneys announced a major offensive against the state's marijuana industry.
MELINDA HAAG, U.S. attorney: One of the reasons we are making these announcements today is to try to put to rest the notion that large marijuana businesses can shelter themselves under state law and operate without fear of federal enforcement.
MICHAEL MONTGOMERY: Targets also include property owners who lease land to growers and distributors. Even newspapers and magazines that carry ads for medical marijuana are under scrutiny.
JOSEPH RUSSONIELLO, former U.S. attorney: The folks who say that they're out there, and here I am and I dare you, they make themselves prime targets by their audacity and by the size of their operation.
MICHAEL MONTGOMERY: Joseph Russoniello served as a U.S. attorney under four presidents. He says advertising is just one indication that most medical marijuana outfits in California are legitimate targets for the feds.
JOSEPH RUSSONIELLO: I think that the U.S. attorneys would probably agree that about 96 to 98 percent of all of the operators and all the dispensaries certainly in the state were out of compliance with the state guidelines, because they were commercial enterprises, because, you know, they were not limiting themselves to people who lived within their jurisdiction.
As soon as you start crossing the county lines and start packaging it and sort of suggesting that your client base or your patients, or your members, really, are all over the state, you're basically in a commercial enterprise for profit.
MICHAEL MONTGOMERY: The crackdown triggered protests and a lawsuit from medical marijuana supporters. They accused the Obama administration of backtracking on what they say were earlier promises to leave states alone when it comes to medical marijuana.
In Mendocino County, officials worry that the raid on Matt Cohen's farm undercuts their effort to strictly regulate marijuana growing.
JOHN MCCOWEN, Mendocino County, Calif.: People are really wondering what is behind this, what happens next, am I personally at risk? We had an individual who is doing everything they can possibly do to be as legal as they could with local and state law, adhering strictly to the letter of the law all the way down the line. So if the federal authorities are going to raid him, then no one is safe.
MICHAEL MONTGOMERY: County Commissioner John McCowen didn't start out as a medical marijuana advocate. In fact, he supported bans on outdoor growing. But he says the county's modest permitting program has helped bring order out of chaos.
JOHN MCCOWEN: By bringing the production of medical marijuana above ground into a strictly regulated program where it's inspected by the sheriff, arguably, tremendously increases public safety and environmental protection. The raid, if it has the impact of driving people out of the program and back underground, will have the opposite effect.
MATTHEW COHEN: Well, here's what's left right there.
It certainly sends the message that the federal government would prefer that collectives and co-ops operate underground, unregulated. It just -- it's appalling to me that illegal farms are existing all around this county and that they're going to come after us.
MICHAEL MONTGOMERY: In fact, local law enforcement continues to target large-scale illegal pot farms. And they're using fees collected from permitted growers to help pay for raids and officer training.
Justice Department officials declined to comment on Mendocino's ordinance. And while the feds have yet to directly challenge the program in court, the recent raids leave the sheriff's department squeezed between local and federal law.
TOM ALLMAN: If the Mendocino County ordinance is in violation of federal law, I want to be told that by the highest court in the land. But if it's not in violation of federal law, I want to be told that too.
JOSEPH RUSSONIELLO: Look, we have consequences. There are things that we have to do to enforce federal law. Whether you're in the way of our doing it or you're halfheartedly cooperating with us or you're indifferent to it, the fact of the matter is, we have federal mandates. We will follow those laws.
MICHAEL MONTGOMERY: Russoniello says federal prosecutors in 15 other states and in the District of Columbia, which also have medical marijuana laws, will be following the crackdown in California closely.