The inspector sighed as she lifted her head from the mess of notes, scribbles and diagrams on the desk. The air in the office was so thick she could barely make up the "no smoking" sign through the mist of smoke.
-"We need some air in here. Gosh, how I hate this man!"
Her sergeant quietly opened the only tiny window in the room. He took a deep breath, relishing the cold, clean winter air as it filled his poor, mistreated lungs.
-"Let's take a step back, shall we?" - said the inspector, gently massaging her tired eyes - "This guy has been missing for months, hasn't he".
-"That's right ma'am. His last activity on a puzzling forum dates back to August, and no one has heard from him since. Back then we realised that one of the other musicians of the chamber ensemble where he played second violin was likely to be responsible, but we couldn't pin it on any of them."
The inspector turned her head to the pinboard, where photos of the suspects seemed to stare at them mockingly:
- Melody Handel, an academic who played first violin.
- Harmon Britten, bricklayer and virtuoso of the viola.
- Viola Mahler, primary school teacher, played the cello.
- Canon D. Pachelbel, a clergyman who played the harpsichord.
-"Months later, while we are at a dead end, we get a message, purportedly from the victim himself. I mean, if you were held prisoner and managed to smuggle out a message, what would you write?"
-"Something very clear, so I can be easily found, surely."
-"Not this guy. He sends us this:"
-"Unbelievable. Does he even want to be found at all?"
-"I'm sure he does, but, from what we've learned of him, he can't be trusted to do the most logical thing at any given time."
Edit: I removed the music tag added after I posted the puzzle. Although there is a musical theme, no specific musical knowledge is needed for the solution.
-Ma'am - The sergeant rushed into the office brandishing a scribbled piece of paper - Constables aznbanana9 and Punintended have had an idea. They seem to be on to something.
The inspector grabbed the note, more brusquely than she would have liked. She perused it intently for a few minutes, then barked:
-Unless it means that he's in space, I don't see how this helps. Unless...
She paused for a moment, then mumbled:
-The great art... ars magna... he's into puzzles, isn't he?
She sat at her desk, grabbed a notebook and started to scribble, to the bemusement of the sergeant.