In January 2014, someone mysteriously attacked Milwaukee Symphony Orchestra concertmaster Frank Almond and stole his 300-year-old Stradivarius violin, worth $5 million. The FBI and Milwaukee police sprung into action and eventually tracked down the violin a week later, when they found it hidden in an old attic.

So, last month, Almond thanked them for getting it back by performing a special concert at Milwaukee FBI headquarters.

Special Agent Dave Bass called the 2014 robbery and recovery of the violin unprecedented. "There are plenty of examples of theft — breaking into a practice room, or the musician accidentally leaves the instrument somewhere — but there has never been an instance I know of where someone walks up to one of these world-class musicians and forcibly takes an instrument. We hope that it never happens again."

The race to find a nearly 300-year-old violin

On the night of January 27, 2014, Almond was attacked with a taser on the way to his car, and a thief stole his Stradivarius violin. When law enforcement found the violin case a few hours later, they assumed the violin was heading overseas for resale.

The Milwaukee Police Department requested the FBI's help, and information about the taser used in the robbery helped agents track down the person who had purchased the weapon — a barber named Universal Knowledge Allah. That lead, in turn, helped the police find other suspects.

At this point, speed was a priority, since the sensitive violin needed to be recovered before it was resold. It also needed to be found before the weather damaged the instrument.

In February, the FBI found the violin and its bows in a Milwaukee attic, wrapped in a baby blanket. An expert who appraised the instrument said it was undamaged, and he even performed an impromptu concert for police to prove it (he selected a piece by Bach).

In May of that year, Allah — the barber who supplied the taser — pleaded guilty to felony robbery and was sentenced to a three-and-a-half years in prison. Another Milwaukee man, Salah Salahaydn, was sentenced to seven years after pleading guilty to theft. He was the prime suspect behind the robbery and had conducted extensive research on Almond and the violin.

Investigators believe Salahaydn was hoping for reward money, rather than to resell it abroad. Salahaydn had previously been linked to a Milwaukee art theft when he tried to sell a sculpture back to a gallery.

Why Stradivarius violins are so valuable

The Stradivarius that Almond plays — on loan from an anonymous donor — is known as the Lipinski Stradivarius. It's one of only a few Stradivarius violins in the world (you can see a partial list of the prized violins and violas here).

Antonio Stradivari and his family are credited with making some of the finest violins and violas of the 17th and 18th centuries. Experts attribute their quality to the unique craftsmanship, wood, and age (even the varnish may contribute to the sound, though nobody has a definitive answer). Though some blind tests have shown that the sound may not be that much better on a Stradivarius than on a similar high-quality violin, the Stradivarius instruments retain their reputation as the best in the world.

$5 million is not at the top of the Stradivarius market. Though recent auctions have failed to break the $45 million mark, it may only be a matter of time. In 2011, one sold for $16 million. Prospective buyers have ample opportunity to pick up a Stradivarius, like in this Sotheby's viola auction this spring.