The suburban Chicago family stole with startling efficiency from toy stores, booksellers and coffee shops from Maryland to Texas, its matriarch often dressed in a bulky black dress outfitted with compartments for stuffing large merchandise, federal authorities said Wednesday.

Lego blocks, expensive dolls, electronics, cosmetics -- even bags of coffee from Starbucks – were concealed under clothing and slipped out of the stores. Little by little, year after year, the three family members were able to make off with millions of dollars of merchandise from well-known retailers such as Barnes & Noble and Toys R Us, fencing the thousands of items on the online auction site eBay, charges alleged.

The decade-long scheme ended after federal authorities say they recently followed Branko Bogdanov, 58, wife Lela, 52, and their daughter, Julia, 34, on a four-day, cross-country stealing spree last month. Agents watched as the Bogdanovs entered stores in Oklahoma, Texas and Louisiana, then exited with Lela Bogdanov’s black dress seemingly bursting at the seams, according to a criminal complaint lodged Wednesday in federal court.

In one stop at a Toys R Us outside New Orleans, agents were watching as a gust of wind blew the mother’s dress open, revealing a package contained in a blue lining “that appeared to be some kind of carrying device,” the complaint alleged.

Prosecutors said over the past 10 years, the Northbrook family -- together with a cooperating individual who acted as its fence -- sold merchandise with a retail value of $7.1 million for a total of $4.2 million through their eBay accounts. Many of the items, such as American Girl dolls, Furby robotic toys and Nanoblock building blocks, were sold in bulk and in their original packaging, the charges alleged.

Frank Benedetto, the head of the U.S. Secret Service in Chicago, said Wednesday the Bogdanov case was noteworthy not only for the extensive financial losses but also for the old-school manner in which the family operated.

“I think they had a system over a significant period of time where I guess they thought they were minimizing their risk,” Benedetto told reporters at his agency’s headquarters in the West Loop. “But eventually law enforcement caught up with them.”

The Bogdanovs were arrested Tuesday afternoon at their upscale, five-bedroom $1.4 million home on Weller Lane. Authorities seized the black dress, the charges alleged.

During brief court appearances Wednesday on a charge of interstate transportation of stolen property, federal prosecutors said they were seeking to detain all three as flight risks. The family is originally from the former Yugoslavia, and it was unclear if any of them are U.S. citizens, according to prosecutors.

At her hearing, which was delayed so a Romani interpreter could be present, Lela Bogdanov sobbed into a tissue and occasionally rested a hand on the lectern for balance. When asked to spell her name for the record, she said she was illiterate, announcing in broken English, “I don’t write…I can’t spell name.”

U.S. Magistrate Judge Michael Mason scheduled a detention hearing for all three on Monday.

Authorities say “organized retail theft” is a multibillion-dollar problem whose and that the costs are eventually passed on to consumers. The thieves, known as “boosters,” often work in groups, targeting multiple stores a day and traveling widely to steal – a mobility that makes cooperation among law enforcement crucial.

“These are not kids stealing some gum or a drug addict taking one item. These are professional crews that are targeting specific property,” said Jack Blakey, who heads the special prosecutions bureau for the Cook County state’s attorney’s office. “It’s difficult for law enforcement to connect the dots if they’re all working independently.”

In a statement Wednesday, eBay praised the work of law enforcement to bring the criminal charges against the Bogdanovs.

The investigation began several months ago after retailers contacted federal authorities about a series of large thefts from stores around the country. By matching up the size and type of merchandise, fraud prevention investigators for the stores and federal agents tracked bulk sales of specific items to one particular eBay account used by the fence.

Authorities confronted the fence – described as a person over 70 with no criminal convictions -- who admitted to having purchased at least $6 million worth of merchandise over the last decade from “Franko Kalath,” an alias for Branko Bogdanov, according to the complaint.

After obtaining court approval for a warrant in order to track a cell phone of one family member, Secret Service agents in several cities were able to follow the three in February as they traveled across the country in their gray Honda Odyssey minivan.

“We had surveillance from Maryland to Dallas, Texas, on these individuals,” Benedetto said. “We used everything from analysis of video surveillance footage to good old-fashioned physical surveillance.”

According to the complaint, agents were watching on Feb. 19 as the Bogdanovs drove to numerous stores and malls in the Houston area. In what appeared to be a coordinated law enforcement move, Houston police briefly pulled their minivan over for failing to use a turn signal after the family was seen leaving a Toys R Us store. When they were asked about boxes of Legos seen in the van, the Bogdanovs said they had been purchased at a flea market and had no receipts, the complaint alleged.

The family handed over to police numerous items they claimed to have purchased at the flea market but didn’t want anymore, including cosmetics, cutlery, and bags of coffee. The police checked their IDs and let the family go. At least five of the stores the Bogdanovs had visited that day later reported merchandise valued at more than $13,000 had been stolen – including Starbucks, which reported eight bags of coffee missing from two stores, according to the complaint.

The next day, agents watching the family leave a New Orleans-area Toys R Us noticed Lela Bogdanov’s “stomach appeared more square or rectangular than unusual, and it appeared that she was holding something against her stomach with her right arm,” the complaint alleged.

Later that day, police in Mississippi pulled the family over for “following another car too closely,” according to the complaint. Branko Bogdanov told the state trooper they were headed back to Chicago from New Orleans and that several large black trash bags stuffed in the van were full of goods purchased at flea markets from “all over.”