‘You always think if you lose something, it’s a catastrophe,’ says the conductor, who will lead the Boston Philharmonic Youth Orchestra this Sunday. ‘But actually, you get another chance to think about it and study it in a new way.’

As he prepares for Sunday’s concert by the Boston Philharmonic Youth Orchestra, conductor Benjamin Zander is feeling both disturbed and excited — agitato, you might say.

That’s because when Zander, who’s 83, takes the podium at Symphony Hall, he’ll be without the scrupulously annotated musical scores he relies on to get the best performance from the orchestra and himself.

The marked-up scores, for Beethoven’s Symphony No. 5 and Strauss’ tone poem “Ein Heldenleben,” have been missing since Zander’s car was stolen — twice on the same day — in Cambridge earlier this month. The white 2019 BMW was recovered (both times), but the scores, which Zander kept in a small black suitcase in the trunk, are still missing.

This isn’t the disaster you might think it is, however. As much as the maestro with the molto-frizzy hair depends on the scores, which he’s painstakingly footnoted over many decades, he’s choosing to view their absence as an opportunity instead of a problem.

“You always think if you lose something, it’s a catastrophe,” says Zander, who speaks with an aristocratic English accent reminiscent of actor John Houseman in “The Paper Chase.” “But actually, you get another chance to think about it and study it in a new way.”

The loss of the scores, whose margins are filled with scribbled words and symbols highlighting the sections Zander believes should be “tender” or “brisk” or “vivacious,” may be a blessing in another way. Media reports about the theft of the car and its contents have generated a lot of publicity for the Boston Philharmonic Youth Orchestra, whose 113 instrumentalists range in age from 13 to 21.

“It’s very funny this has become such a cause célèbre,” said Zander, who founded the Boston Philharmonic Orchestra in 1979 and the youth orchestra a decade ago. “I went to a concert (Wednesday) and everybody was saying, ‘Oh my God, I’m so sorry,’ as if I’ve lost a member of my family.

“But they all know about Sunday’s concert now!” he said, laughing.

Cambridge police say they expect to make an arrest soon. “We have a good sense of who’s behind this,” said Jeremy Warnick of the Cambridge Police Department. “It appears to be a case of the type of vehicle, not what was inside or who owned it.”

But they’re not so optimistic about finding Zander’s prized transcriptions, which were ditched sometime before the car was discovered (twice) in Allston.

The scores have no value to anyone but Zander, who had spent countless hours over many years annotating them, using colored pencils to accent virtually every measure of the music. The Strauss piece, which the BPYO has been rehearsing for two months, is particularly complex. It’s the story of a hero and his wife, and Zander’s score was a jumble of lines and dots and words like “frivolous,” “sharp,” “shrewish,” “angry,” and “loveable” to describe the mood he wants the music to convey.

“What I’d done is fill it with markings in color so that, like a GPS map, it tells me where to go,” he said.

Iverson Eliopoulos, an orchestral conducting student at New England Conservatory of Music and a former cellist in the BPYO, said most compositions performed by the orchestra are centuries old, but Zander treats them as very much alive.

“Ben’s been using the same physical copies of these scores for decades because he’s always finding new ideas or new interpretations of the music,” said Eliopoulos. “He’s been building on these ideas for many decades and they’re all carefully marked up on every single page of the score.”

BPYO concertmaster Nikki Naghavi said the orchestra is enormous — there are 42 violins alone — but it’s been rehearsing long enough to know exactly what Zander wants.

“Still, the score is like a great novel,” Naghavi said. “Every time you read it, you take something else out of it. Ben had put all these ideas together, and for that to be gone now is absolutely shocking.”

Upset at first, Zander said he’s actually looking forward to performing without the old scores. In recent days, he’s been poring over new copies, frantically marking them up with his colored pencils. His optimism is striking. Is it possible the car heist was an inside job, a PR stunt staged not only to fill seats on Sunday but to give the conductor an excuse to relearn the score?

Zander erupted in laughter.

“I don’t think I would have the ingenuity to think of that,” he said.