According to Atchison Police Chief Mike Wilson, a motorist saw someone sitting on the edge of the bridge shortly after 1:15 a.m. and notified Buchanan County authorities. Upon arrival, they discovered the person was no longer on the bridge.
An abandoned car was found on the bridge which was traced back to a 23-year-old Atchison man. Police believe that is the man who may have jumped.
Multiple rescue agencies searched the area throughout the day.
A separate crew was further down the river near Leavenworth searching.
Ken Reeder, a St. Joseph resident, was in the area on Saturday night and saw the police presence.
"Late last night there were police vehicles of all types on top of the bridge almost all evening," he said.
Crews have used sonar to map the bottom of the river.