SCREAMS IN THE NIGHT

Everyone was still frightened when the police began to question to the people. Everyone loved Frank, except one: a violinist,Ian, that, like Frank wanted became the first violin of the orchestra. It can be convenient kill him to reach his purpose; moreover Marilyn found Ian's pen near the corpose. Immediately the police arrested him.
So I returned to my bedroom and my phone rang. I picked up the receverand...

"Hey, boss, the police has arrested Ian. Great plane"

What did it mean? Who killed Frank?

By maddalena