An argument on a 44 bus on Humboldt Avenue this morning ended in a bloody knife fight that left one person dead, according to the MBTA and the Boston Police Department.

The fight erupted around 9 a.m. as the bus neared the Trotter School, 135 Humboldt Ave.

A nurse at the school rushed outside and performed CPR on the more seriously injured person, but he died. The Boston Herald reports police are looking for four suspects who fled the bus.