A fatal plane crash in Watertown, Wisconsin, claimed the lives of a 73-year-old pilot and his 8-year-old grandson joining him for a flight up to northern Wisconsin.Summit View Elementary School sent a letter to inform families about the tragic loss of student Colin Strebe on June 14 due to an accident.The aircraft plunged into a grove of trees at Brandt Quirk Park near a residential area on Wednesday at approximately 9 a.m. Investigators spent much of Thursday at the site, where pieces of the wreckage were spread across the soccer field.The National Transportation Safety Board and the Federal Aviation Administration were at the airport hangar to examine the evidence. According to reports from Federal Aviation Administration, the plane had just taken off from the Municipal Airport about 3 miles from the accident site. Sources say the flight was planned to Manitowish Waters.Investigators will collect as much information as they can from witnesses, and the wreckage itself, to determine, if they can, what led to this family tragedy in Watertown.Watertown police department said the Brandt Quirk Park would remain closed through the weekend for site cleanup.Police have yet to identify the victims, officially saying only that there were two victims. The pilot is from Watertown, and his grandson is from Waukesha.The FAA and National Transportation Board will lead the investigation. WATCH: Scary moment for Watertown neighbors who heard and 'felt' the plane crashTOP STORIESHungry bear eats employee's lunch in company truckFox Point pool will be closed for the summerCheap Trick cancels Summerfest performance