The bodies were found Tuesday morning in Romero's parked car in Chicago's Brighton Park neighborhood.
Police say Romero and Alequin were found in the car's back seat and both had been shot multiple times.
The medical examiner's office did not list a cause of death for Butron, whose body was found in the trunk.
The bodies were found shortly before 7 a.m. in an industrial area.
The white Toyota Avalon was parked in the 4800-block of South Whipple and was moved four hours after the bodies were discovered.
The car was parked outside AccuLabs, a supplier of specialty chemicals to the plating and metal finishing industries. One worker described the area as typically desolate early in the mornings.
Because of all the police activity, AccuLabs had to let a shift go because their entire working area was crowded by police activity. Workers said they couldn't get $100,000 worth of shipments of their products out the door.
The discovery of the bodies came less than a month after three bodies were also found bound and gagged in a car in the McKinley Park neighborhood. Both cases are being investigated.
On Tuesday, the family of Romero identified him, saying he was a father of three who at one point worked for the anti-violence organization CeaseFire.
Residents described the area as dangerous.
"It's really bad. Gang bangers around, and kids won't come out and play because they are chasing each other, throwing gang signs," said Maria, Brighton Park resident.
Romero lived in the Humboldt Park neighborhood with his relatives, including his aunt. Wanda Romero, who says he was like her son. Overcome with grief, she was treated in the home by paramedics. More relatives in Romero's close-knit family flocked to the home including a cousin who was told about the death and came home early from high school.
Romero's father, who the family said is sick, didn't take the news well either, with paramedics being called to the house again.
Relatives said Romero was a responsible stay-at-home dad.
"We were at a family party in the back yard, and he was OK, laughing with the kids. Next thing you know, we hear this," said Jeannett Gonzalez, Romero's cousin.
Chicago Police Superintendent Jody Weis said it's possible the crime is drug related.
"It has certain similarities to the case of last month where they were three bodies found in a car. We don't know any more at this time," said Weis.
The Associated Press contributed to this report.