It is not clear if the victims knew their killer.
Friends of the couple said they had just moved into the third-floor apartment a few months ago. Neighbors say the building is normally quiet.
"Yes, I heard shots, two shots, real loud. After the shots, a guy came down, running real fast, running that way and up the alley," said Gloria Rivera, neighbor, who has lived there for 40 years.
Police say the suspect- a man- broke into the apartment and shot the victims; They were both pronounced dead at Illinois Masonic Hospital.
"They were good people, always a couple, nothing separated them," said a friend of the couple who did not want to be identified.
Santiago was a construction worker who was going to business school. Escobar had hoped to start a family, friends say.
"I really don't know who would do this to them, but it's crazy. They were lovable, caring and always there when somebody needed them," said the friend.
Other friends were at the crime scene, gathering belongings. None wanted to talk publicly- and some of their friends covered their heads from cameras.