New York ? A no-cutting-in-line conflict between two large groups of shoppers helped to spark the Black Friday stampede in which a Wal-Mart worker was trampled to death, Nassau police said Wednesday.

Shoppers who remained inside their vehicles in the parking lot until the Valley Stream, N.Y., store’s special 5 a.m. opening apparently clashed with people who had stood in line for hours outside Wal-Mart, police said.

When the store’s doors opened, the conflict between the two groups — with “a considerable amount of people” who had stayed in their vehicles rushing to enter the store without waiting in line — fostered “mob mentality,” Nassau Police Lt. Kevin Smith said.

In the crush of an estimated 2,000 people, the set of doors was broken and Jdimytai Damour, 34, of Jamaica, a temporary security worker, was trampled, dying of asphyxiation, police said. No one has been charged in connection with the death, though police are investigating possible criminal charges.