He was 68.

The cause of his death is still not known.

With a black and white image of the guitarist, the group wrote on X: "#JackSonni Rest In Peace #DireStraits."

Born in Indiana, Pennsylvania, USA, Sonni was best known as "the other guitarist" in Dire Straits during the band's Brothers in Arms era. 

During his early life and education, Jack learned piano, and trumpet, and later to play on guitar. In the fall of 1977, Jack went to work in Manhattan, as per the official website of Dire Straits Blogs.

Later in 1978, he started working at the newly opened Rudy’s Music, owned by Rudy Pensa, where he met members of Dire Straits. First, he met with David Knopfler and then with Mark Knopfler.

In 1984 Jack was a part of the recording session for Brothers in Arms album, as well as he played guitar synthesizer on “The Man’s Too Strong.” Sonni was also on the stage during the Dire Straits’ world tour BiA in 1985-86.