Dimova was a lawful permanent resident.  She worked at a hospital with a man named Mihaylov at a hospital in North Carolina.  Mihaylov eventually moved to Canada.  Later, he asked Dimova to help him by driving his family from Canada to the United States; he cited a back problem as the reason he couldn't make the long drive himself.  As the group approached the border, Mihaylov and his wife tried to leave the car and implored Dimova to use certain documents to get their child across the border where she could pick them up.  Dimova refused, and left all three Mihaylovs in Canada, before driving the car across the border.  After re-entering the United States, she became concerned for the well-being of Mihaylov's small child, and proceeded to the rendezvous point on the United States side of the border.  Subsequently, they were all apprehended by Border Patrol officers, and Dimova was charged with removability for alien smuggling.  Though recognizing the untenable position that MIhaylov placed Dimova in with respect to the safety of the small child, and recognizing that Dimova did not intend to engage in alien smuggling while in Canada, the Immigration Judge found that Dimova's act of picking the Mihaylovs up at the rendezvous point constituted encouragement, inducement, or assistance in alien smuggling.  The Board of Immigration Appeals affirmed, concluding that by returning for and picking up the Mihaylovs, all the while knowing they had entered the United States illegally, Dimova affirmatively assisted the Mihaylovs' illegal entry.

On appeal, the First Circuit agreed that Dimova did nothing in Canada to encourage, induce, assist, aid, or abet the Mihaylovs' crossing.  Nevertheless, the Court found that the Mihaylovs had not completed their entry into the United States at the time Dimova picked them up.  "Although there is no evidence showing the Mihaylovs were under surveillance from the time they crossed the border to the moment of their arrest mere hours later, the record demonstrates the Mihaylovs did not exercise their free will in any meaningful way after their physical crossing. The only thing the Mihaylovs did in the United States was wait overnight, in a remote wooded area, for Dimova to pick them up. All told, they were in the United States for a matter of hours, just a walk from the border, before Dimova rendered the assistance necessary for them to move forward with their effort to enter the country without apprehension.  Moreover, the group's apprehension occurred in Vermont, long before they arrived at their planned end-destination in North Carolina. Accordingly, we can not say on these facts that the Mihaylovs' entry was complete at the time Dimova came back for them."

The court declined to establish any bright-line rules for when an entry is complete, instead confining its ruling to the facts before it.  

The full text of Dimova v. Holder can be found here: http://media.ca1.uscourts.gov/pdf.opinions/13-1550P-01A.pdf