Grant Ward did not just kill his brother; Ward killed a [fictional] United States Senator.
Grant Ward already has a huge list of victims that would be a series of long murder and treason trials. Kidnapping and murdering a United States Senator has its own enhanced punishments in Federal Court. 
Grant Ward beat Senator Ward, killed at least two guards, and tortured the Senator with the forced digging up of a buried well, followed by threats to throw the Senator down the well.
Federal Prosecutors could prove beyond a reasonable doubt that Grant Ward killed his brother with malice aforethought that included kidnapping and torture. 18 USCS § 1111.
There is very little a defense attorney could do for Grant Ward, other than try plea-bargaining for life in prison over the death penalty. Given the number of people Ward killed (at least five SHIELD Agents, four soldiers, two guards, and a Senator) plus the charges for treason by working with HYDRA, it is hard to imagine a Prosecutor even entertaining the idea of a plea; the literal bodies of evidence should end a trial with the death penalty for Grant Ward.