EXCLUSIVE: The public needs to be cautious about speculating on a motive for Sunday evening's Christmas parade horror in Waukesha, the president of the Wisconsin Fraternal Order of Police told Fox News in an interview .
"Hours later, everything is still very fluid, right now," Ryan Windorff said late Sunday.
"There are a countless number of witnesses that need to be interviewed," Windorff said. "Even if somebody didn't witness something firsthand, they may have video on their home or business surveillance system that is going to benefit the investigation."
Video that circulated on social media shortly after the incident showed spectators standing along the route of the annual Christmas kickoff event as a maroon-colored Ford SUV careened through the parade line.
Law enforcement will now begin to develop a timeline of events to track the activity of the person believed to be driving the SUV, Windorff said.
"Law enforcement is going to want to retrace the incident from the first sign of it at the parade, but even go back before that in the days and weeks before leading up to it," he explained.
Waukesha police Chief Dan Thompson said late Sunday that a person of interest was in custody and that police had recovered the vehicle believed to be used in the incident. Police did not immediately disclose a possible motive.
WAUKESHA CHRISTMAS PARADE: 5 DEAD, 40 INJURED AFTER SUV PLOWS THROUGH WISCONSIN CROWD: LIVE UPDATES
"I think at this point the terms ‘suspect’ and ‘person of interest’ are probably interchangeable," Windorff said. "If there is a motive that is even determined, it will be released. But, I would just caution people to not jump to conclusions."
According to Waukesha city officials, the incident resulted in at least five deaths and more than 40 injuries, with some of the victims being children.
Local police showed up for work Sunday expecting a simple, peaceful parade assignment – but it turned into a nightmare scenario, Windorff said.
"This is a worst-case, horrific situation for law enforcement. They're working parade duty essentially. It should be an easy day … and in a blink of an eye it turns into a horrible tragedy," he said.
Despite the gruesome scenes on the ground, Windorff told Fox News that the brave actions by police, first responders and ordinary citizens offered a silver lining during a challenging time for the community.
"In a horrible situation like this, I think some solace can be seen in acts of selflessness that we saw tonight in Waukesha."