(CNN) -- More than 400 tips came in Wednesday as authorities conducted an intensive manhunt for a gunman suspected of killing one man and wounding three others in a two-state rural shooting rampage south of Chicago, Illinois.
"We have a very dangerous situation," Sheriff Rogelio "Roy" Dominguez of Lake County, Indiana, said late Tuesday. "We want to report that the suspect is still at large and that he is armed and dangerous."
Authorities are concentrating their efforts in the southwest portion of Lake County, the county's chief of police, Marco Kuyachich, said Wednesday afternoon.
A police artist is talking with a farmer who was shot, Kuyachich said, and they hope to develop a better sketch of the man, who is described as a heavyset 30- to 40-year-old male with short brown hair. He was wearing a baseball cap, a blue-green jacket and light-colored jeans, and was last seen driving a white or gray Ford or Chevy full-size pickup, police said.
The shootings began about 10:30 a.m. at a construction site near Beecher, Illinois. The gunman killed one worker at the site and wounded two others, Dominguez said.
One of the wounded men was in critical condition at a Chicago hospital.
An hour later and about 10 miles away in Lowell, Indiana, authorities believe the same gunman opened fire again -- this time on a local farmer.
Keith Dahl was shot in the left shoulder, arm and elbow before he was robbed.
Dahl told Lake County Sheriff's Detective Robert Martinez that the suspect approached him on his farm and started a conversation about bees before opening fire.
The suspect is believed to be using a revolver -- possibly a Colt .38 or .357 Magnum -- because no shell casings were found at either scene, according to Dominguez.
"We'll use every effort to apprehend him," Dominguez said. "Every law enforcement tool will be used to capture him."