COLUMBUS, OHIO ? A weekend fire that killed five college students in a house near Ohio State University was arson and the deaths are being treated as homicides, investigators said Tuesday.

Authorities had not determined a motive and have no suspects, Detective Mike McCann said. A $15,000 reward was being offered for information leading to an arrest.

Investigators wouldn’t comment on what evidence had been gathered.

Sunday’s fire in the three-story brick house near campus killed two Ohio State students and three students from Ohio University. Two more students remained hospitalized Tuesday, one in critical condition.

Investigators ruled out an accident after scrutinizing a full-sized charcoal grill that had been on the wooden front porch, and gas and electrical lines leading to the house. Some witnesses said they heard glass breaking and what sounded like a pop around the time the fire began.

The fire broke out after a 21st birthday celebration for Alan Schlessman, one of the victims.

The victims were found on the second floor, where bedrooms are located.