It's a heartbreaking Christmas for a Brooklyn family. 

Marcin Iwanowicz, 46, was fatally shot Christmas Eve morning outside a rehab facility. 

Police don't have a suspect in custody, and the victim's father tell CBS News New York he does not believe his son knew the victim. 

"He help me with the shopping, with everything. This is my like right hand. I am too old, I can barely walk," Stanislav Iwanowicz said. 

Stanislav Iwanowicz spent Christmas Eve preparing a holiday feast for his two sons in their Midwood apartment only to find out Christmas Eve the older one would never come home. He said police told him his son was fatally shot in the chest just before 10 a.m. outside the St. Jude Treatment Center in Brownsville. 

"They said, you know, that he came from the clinic and he argue with some guy, you know, because they ask for some money or something, and he said that he doesn't, give you know because he doesn't have any money," Iwanowicz said. "And then somebody pick up the gun and shoot him." 

Police said Marcin Iwanowicz was taken to Brookdale Hospital, where he was pronounced dead.

On Christmas Day, his scooter was still outside the clinic, and there was what appears to be a bullet hole outside the building where the father said he went for methadone treatment Wednesday, something he'd done daily for years after, his father says, he became addicted to painkillers after a should surgery. 

"He get sick and because he just have Medicaid they sent him for methadone program," Stanislav said. "Then the program on Coney Island was closed, then he find what was open." 

There are surveillance cameras around the building. The NYPD says the investigation is ongoing. 

NYPD sources said the shooting may have stemmed from a physical dispute, and that the suspect was dressed in all black with a yellow hooded sweatshirt. 

Iwanowicz wants to see an arrest, saying his son doesn't deserve this. 

"Very nice guy. He was friendly. He help everybody. This is my neighbor that came over and he knows him. He was good guy. He get good heart all the time," he said. 

On this holiday, the devastation difficult to bare as he also lost his wife several years again in a car accident. 

"Nine kids. Some kid was driving by the car, and hit her. After six days, she died. You know - my son died, and it's time for me to be dead," he said. 

Iwanowicz said he brought the family here from Poland for a better life, and now, as he himself faces health issues, he can barely afford his apartment.