Manzanita-Mohave Residence Hall's 40th anniversary celebration was nearly interrupted by the work of an arsonist Friday.

An early-morning fire charred part of the lobby of the hall, 1000 N. Park Ave., after someone ignited a poster board behind the front desk Friday, one day before the conclusion of the anniversary celebrations.

University police and the Tucson Fire Department arrived to find the fire extinguished but the lobby filled with smoke.

A witness told police she was returning from work at 4:05 a.m. and saw the fire behind the desk, university police Sgt. Brian Seastone said. She also reportedly saw a male leaving the hall as she walked in.

Seastone said another witness reported that she saw a male behind the front desk shortly before the fire started.

Police have classified the fire as an arson and have a suspect in the incident, Seastone said. He would not comment further on the case.

Kirk Sibley, the 40th anniversary coordinator and a hall resident assistant, said the fire did not impact the celebrations. The lobby was aired out and all damage painted over by mid-afternoon Friday.