Bruno was an assassin for the military until he grew too obsessed with his work and started designing more and more creative ways to kill people.
After S.H.I.E.L.D. added his name to the Index, they imprisoned him in Brynmore Psychiatric Hospital.
Fight On Edit
In "One of Us", Bruno escaped after Cal broke into the hospital. He attacked Bobbie and Coulson, but Bobbie quickly got the better of him and subdued him.
The nature of the ability that got Bruno on the Index is not specified.