UPDATE: The investigation continues into Thursday's fatal crash on Interstate 75.



Preliminary reports suggest a semi-truck traveling northbound near Ooltewah was unable to stop and hit 8 vehicles in a construction zone.



Six people were killed in the crash, including two children.



Channel 3 was contacted by the youngest victims' grandmother. She lives in Seattle and tells us the girls, ages 9 and 11, were in Tennessee visiting with their mother and her family.



After that visit -- they were going to fly to be with her in Seattle for the rest of the summer.



Sadly, that visit will not happen.



"We have a hard time understanding why he (the driver) could not see all those cars stopped in front of him," said Grandmother Kristi Garrigues.



Among the crash victims are sisters Kelsie and Savannah Garrigues from California.



Their mother and grandmother had just picked the girls up at the Atlanta airport for a six week visit.



Their paternal grandmother lives in Seattle, Washington.



Kristi Garrigues says the girls, ages 11 and 9, loved the outdoors.



"They loved being at the beach, they loved boating, they loved hiking quite often," Garrigues said, "They were totally outdoor girls."



Police say the driver of a semi-truck was unable to stop and crashed into 8 cars on 1-75.



Savannah and Kelsie Garrigues passed away along with their mother, Tiffany Watts, and grandmother Sandra Anderson.



Chattanooga police are now asking anyone who witnessed the crash -- to give them a call.



"We're using these callers to verify a lot of what we know, and we're also using these callers to elaborate on what we might not know yet," said Lt. David Gibb, Traffic Division of Chattanooga Police Department.



Investigators are now collecting crash data from all of the cars and semi-truck.



That information will tell the investigators if the brakes were working properly, when or if they were applied, and how fast the truck was going.



Police believe a man was driving and he had a female passenger on board.



"Based on the location of injury on the two parties in the vehicle and the damage inside of the vehicle, it's pretty fair to say that he was driving the vehicle," said Lt. Gibb.



The truck driver was interviewed after the crash and a blood sample was taken to test for any drugs or alcohol.



Those results have not come back yet.



"He appeared to be not quite right, but it's very hard to elaborate on that without seeing the blood work because everybody acts different."



Kristi Garrigues says the family is having a hard time accepting the girls are gone.



She wants to know what happened, why the truck did not stop.



The driver of the truck has returned home to Kentucky.



He has not been charged with a crime.



Investigators spent the day Monday completing inspections of the semi-truck and should have results sometime Tuesday.



Stay with Channel 3 for those results.