HAPPY VALLEY, Ore. -- Authorities are searching for a man who they say set another person on fire at a Happy Valley Denny's restaurant Wednesday night.

The Clackamas County Sheriff's Office told KGW's Mike Benner the man walked into the restaurant, located at 12101 Southeast 82nd Avenue, at about 9 p.m., sat down, threw gasoline on the customer, then lit the victim on fire with a book of matches.

The suspect left the restaurant and ran south on Southeast 82nd Avenue.

The victim is a 69-year-old man. He is in critical condition at Legacy Emanuel hospital.

Deputies said the suspect and victim did not know each other.

The suspect was described as 5-foot-10 to 6-feet tall with a medium to muscular build and a lighter-skinned complexion. He's in his mid to late 20s, wearing a black flat-brim hat, black hooded jacket, gray sweatpants with a black stripe, and black shoes.

"It’s ridiculous! I have no idea what to think about that,” Jesse Loyer told KGW.

He visited Denny’s with his grandmother in the morning, and saw the burned booth.

“You wonder what’s going through the suspect’s head to do that to a complete stranger. My thoughts go out to this guy’s family, and I hope for a fast recovery.”

Detectives are looking into the possibility that this case is related to another incident earlier this week, in which a person threw gasoline on a stranger at the Clackamas Town Center movie theater.

Deputies told KGW Thursday that they did not make the incident public based on an interview with the victim, who seemed to treat the incident as a joke. They will now interview the  person again.

Denny's issued the following statement Thursday morning:

“We are deeply disturbed by the senseless, random act of violence that took place at our franchised-owned Happy Valley restaurant, and our thoughts and prayers are with our guest that was seriously injured. Both guests and team members acted quickly to help this guest and ensure the safety of others in the restaurant. We are actively assisting authorities in their investigation and we ask that anyone with information to please contact the Clackamas County Sheriff's office at 503-723-4949."

The Clackamas County Homicide and Violent Crime teams are investigating.

Anyone with information about this case is asked to call the Sheriff's Office Tip Line at 503-723-4949 or by filling out the online form. Click here to fill out the form and reference CCSO Case No. 17-10537.