Aldo (last name unrevealed) is an Italian immigrant afflicted with a severe condition known as Fatal familial insomnia. He was a witness to the assault of Jerry Bullard, who ran into Aldo covered in blood, by his wife Jane, who attacked Jerry while drunk over being a victim of embezzlement.
Aldo's insomnia caused him to lose track of time and led to multiple police reports by his neighbors. It got so severe he cut two of his fingers off by accident at the butcher shop, his wife left him, and he would aimlessly stumble the streets sleep-deprived, being nicknamed "The Night Stalker".
He was taken into custody on suspicion at first, but Dr. George Huang diagnosed him and he was brought back to the scene, where he was an invaluable witness in the assault and even pointed to the swingers' club, The Swing Set, the Bullards would frequent and had the fight nearby.
Huang hospitalized Aldo to confirm his diagnosis and try to maintain his dwindling health. Not wanting to devastate Aldo over the condition usually being fatal, he promised to do what he could medically. (SVU: "Bombshell")