Questions remain in deadly Florida highway crash (AP) - Just hours before a pileup that killed 10 people, authorities had closed a stretch of highway smothered in smoke and fog due to a three-vehicle crash that left a passenger seriously injured. Why they reopened it just minutes before the second crash - and who made the call - remained murky Monday, with the Florida Highway Patrol refusing to answer questions as national investigators hinted they might join the inquiry. An FHP report noted that police closed Interstate 75 about midnight Saturday following the smashup between two SUVS and after drivers called in reporting low visibility. They reopened the roadway at 3:30 a.m. - 15 minutes before at least a dozen cars, six tractor-trailers and a motorhome collided south of Gainesville, pushing some of the cars under the crushing bellies of big rigs, causing others to burst into flames and sending metal shrapnel flying through the air. Eighteen survivors were hospitalized. FHP spokesmen at the state and local level did not respond to several phone calls and emails Monday from The Associated Press seeking answers to what protocol authorities follow - and whether it had been altered following a similarly deadly crash in 2008 on Interstate 4 between Orlando and Tampa, about 125 miles south of Sunday's crash. Four people were killed and 38 injured in that crash. Meanwhile, the National Transportation Safety Board sent investigators to Gainesville on Monday to determine if it would formally join the inquiry into the crash and its causes. Either way, the highway patrol will remain in charge of the investigation, NTSB spokesman Peter Knudson said. "We've investigated a number of these pileups and we just want to see if there is any lesson we can learn from this particular series of accidents," he said. One of the areas that our investigators will be looking at is the reopening of I-75. The pileups happened on both sides of the highway. When rescuers first arrived, the smoke and fog were so thick the only way they could locate victims was by following the sound of their screams and moans from the wreckage, which was strewn for nearly a mile. Authorities had not released the names of the victims, but did say that four people died in one of the cars and that a "tour bus-like" vehicle also was involved in the pileup. The fog and smoke had cleared enough Monday to reopen all lanes of the roadway. Steven R. Camps and some friends were driving home hours before dawn Sunday when they were drawn into the massive wreck. The fire that is believed to have contributed to poor visibility on the highway had destroyed 62 acres and was still burning Monday. Florida Forest Service spokeswoman Ludie Bond said the fire began Saturday and investigators were still trying to determine whether the blaze had been intentionally set. No home are threatened by the fire. ___ Associated Press writer Freida Frisaro in Miami contributed to this report.