Prosecutor Jason P. Hernandez told a jury yesterday there was no plausible legal justification behind a billion dollars in illegal tax shelters marketed by BDO Seidman, Jenkens & Gilchrist and Deutsche Bank Alex.Brown.

Launching a three-month long trial in the hopes of convicting five defendants, Mr. Hernandez laid out an extended scheme to manufacture paper losses for some 1,000 wealthy clients under the cover of opinion letters issued by Jenkens & Gilchrist and former firm partners Paul Daugerdas and Donna Guerin.