Venco was corrupt, and took bribes; for this, he was arrested by his brother, expelled from the Guard, and sent to a prison world. There, he caught a terminal disease that was incurable by bacta or any other medical technology. He also experienced a new purpose of sorts: deciding that the Republic was corrupt beyond all repair, he wanted to try and assure its demise before he died.
In 23 BBY, Sagoro was assigned to investigate the assassination of Senator Jheramahd Greyshade while the successor, Simon Greyshade, was placed under the protection of the Jedi Knights. His investigation would eventually implicate his brother in the crime.
Venco then used his nephew Reymet's naïveté to get his hands on Sagoro's Senate access code. With these codes, Venco entered the Senate for one final assassination attempt against the new Senator Greyshade.
As soon as Venco was implicated in the plot, Sagoro was taken off the case as the investigation turned toward the Autem family. Sagoro's commitment to protecting his charge, however, never wavered. Defying orders, Sagoro was there when Venco fired his shot. Greyshade lived, but Sagoro was forced to kill his brother, effectively eliminating his one chance to clear his involvement in the crimes.
- The Complete Star Wars Encyclopedia