National Transportation Safety Board investigator Edward Malinowski said Sunday that it could take six months to a year to determine what caused the aircraft to crash and then burst into flames next to a feed store.
Malinowski said investigators are examining the Piper PA-24 aircraft's frame and its single engine, as well as any marks left by the plane.
It happened just after noon in Spring Branch, Texas. Investigators say the single engine plane took off from Kestel Airpark and crashed shortly after near Highway 281. The plane ran into a fence before going into a brushy airway.
"We do know that the plane made a dive downwards. We don't know the reason why. We don't know the extent of the aircraft's condition. All we know is that it did end up in this location and as a result four were killed," said Trooper Deon Cockrell with the Texas Highway Patrol.
The Comal County Sheriff's Office identified those killed as 38-year-old pilot Michael Scott Galloway of Spring Branch, his 32-year-old wife Heather Louise Galloway, their 10-year-old son Clayton Galloway and their eight-year-old daughter Cheyenne Elizabeth Galloway.
The Associated Press contributed to this report.