Five Equal Parts - A Musical Mystery #1010888

Every morning, five conservatory students shut themselves away in a parish auditorium to rehearse for an international competition. A flute, an oboe, a clarinet, a horn, a bassoon. Five equal parts — that was what they had agreed the summer before.

That Saturday morning, four of them cross the square for a break at the bar. They are gone for thirty minutes. When they come back, the fifth is dead.
None of the four was in sight the whole time. None of the four is telling the whole truth.