Jeremy Wash was the attorney of death row inmate Douglas Pfeiffer. He brought the mother of Douglas Pfeiffer, Alberta, to the Lone Gunmen seeking their help to save her son. His client had abandoned the appeals process and was giving up.
However, this was exactly what Wash wanted. Douglas Pfeiffer was a hitman and his attorney was the man who employed him. He sent him out to kill people who wouldn't sell in the downtown area that Wash was trying to develop into high rises. So his acting as the man's attorney was to keep the hitman under his thumb even in prison.
Jeremy Wash awaiting his own execution in Death Row.
Wash learned that the Lone Gunmen were trying to convince Pfeiffer to confess about Wash's involvement so he contacted another inmate, Lowry, to have Pfeiffer killed. While Byers' convincing failed, it was Lowry's attempt on his life that made Pfeiffer turn on his boss. Wash was arrested by Texas Rangers at Death Row while his former client watched him.
As Pfeiffer later marches off to his execution, he passes by his ex-attorney, which reveals Wash ended up on Death Row himself for his crimes.
(The Lone Gunmen: Maximum Byers)