MARION TOWNSHIP (AP) — Investigators believe some jewelry robbers followed their victims for several hundred miles from a trade show in Chicago before they struck at a rest stop in Minnesota.

Olmsted County sheriff's officials say four people dressed in black got out of a van at the Interstate 90 rest area near Rochester early today, smashed several windows on the victims' vehicle and grabbed three or four suitcases filled with gold and silver jewelry and loose diamonds.

Capt. Scott Behrns says the value of the loot is at minimum $500,000. Seven people were traveling together in the vehicle from the trade show and stopped at the Marion Township rest area.  Two people stayed with the valuables while the others used the facilities.

Behrns says the victims were apparently robbed "at the earliest opportunity." The suspects remain at large.