James A. Buck gladly accepted the package at his Parkville office from the deliveryman wearing a UPS uniform.

But minutes later, police swooped in to arrest Buck, 54, and seized the parcel, which had contained three pounds of marijuana he sent to himself from California, according to court records. Buck pleaded guilty to a possession charge, though he said in a recent interview that the drugs were for medicinal use.

Buck's case and search warrants unsealed last week offer a glimpse into a long-standing — and growing — smuggling practice: mailing drugs from California to Maryland.

"It's very easy to do without it being detected just because of the sheer volume of mail," said Neill Franklin, a former Baltimore police major and executive director of Law Enforcement Against Prohibition, a group that advocates legalizing and regulating drugs. "It's worth taking the chance to do it: It sure beats driving, and you definitely don't want to get on a plane with it."

The U.S. Postal Service and private parcel services have become popular shipping choices for traffickers as drug laws have evolved. California became the first state to legalize medical marijuana more than 15 years ago, and dispensaries have proliferated there. Meanwhile, more than a dozen states have followed suit, and last month Colorado and Washington state voters approved ballot measures legalizing recreational marijuana.

It was not the first time Buck, who described himself as an advocate for legalizing marijuana, had tried sending himself a marijuana stash. He said he typically triple vacuum-seals it to avoid detection by drug-sniffing dogs. He also believes that marijuana residue can remain on a package if smoked while packing it.

In Buck's case, authorities had already confiscated most of the marijuana and then set up the delivery as a way to arrest him, posing as a regular UPS courier, according to a warrant. The United Parcel Service and other private carriers work with federal officials on investigations; in this one, the Drug Enforcement Administration was on the case.

Last week, about 20 federal search warrants were unsealed in Baltimore, providing details on how law enforcement cracks down on mail schemes. About half of the packages from California were suspected of containing drugs and the other half contained money being sent back to that state.

On a busy Thursday in August at a Linthicum Heights U.S. Postal Service processing facility, Diesel, a Montgomery County police drug-sniffing dog, located parcels that were later shown to contain two kilograms of cocaine and more than eight kilograms of marijuana, according to the court documents.

One of the packages contained 515 grams of marijuana nestled in two cereal boxes. Other shipments were wrapped up with clothing.

The following month, Diesel and Ace, another dog, were set to work sniffing out cash and found packages containing almost $100,000 that investigators suspect was payment for mailed drugs.

"Express Mail and Priority Mail services are regularly used to ship controlled substances and bulk cash through the U.S. Mail," postal inspector Christopher Callahan wrote in the search warrant applications.

Callahan added that investigators also look for certain California ZIP codes in the return address and check the parcels' weight. If an initial screening raises suspicions, the dogs are brought in.

Senders often try to fool authorities by using false names, so that the names and addresses on packages don't match, making suspects harder to track down and sometimes drawing unsuspecting recipients into the schemes.

In 2008, Cheye Calvo, mayor of Berwyn Heights in Prince George's County, unwittingly accepted a package stuffed with marijuana and sent to his house. Officers raided Calvo's home and shot his two dogs. Later, the county police chief described Calvo as an "innocent victim" of a trafficking scheme.

Frank Schissler, a spokesman for the U.S. Postal Inspection Service, which investigates crimes that use the mail, said one case was referred to local law enforcement in the time frame covered by the warrants. He declined to comment further on the investigation.

Postal inspectors arrested 1,327 people nationally for sending drugs in the mail and seized $14.6 million in proceeds in fiscal 2011, the latest year for which statistics are available. By comparison, in fiscal 2007, 860 suspects were arrested for drug trafficking via the mail, and $3.8 million was seized. The inspectors often work with local police on the cases.

"There is an increase that we're trying to address through our proactive efforts with other law enforcement agencies," Schissler said.

Private carriers also have their own security measures.