Updated 09/29/11 – 4:14 p.m.

CHICAGO (CBS) — Police are seeking two brothers for questioning in a shooting that has now left a 15-year-old boy dead in the East Garfield Park neighborhood.

Antonio Johnson, 15, was Antonio Johnson was declared brain dead Sunday night at Mount Sinai Hospital, after being shot at 4 p.m. that day outside his home in the 700 block of North Springfield Avenue. He was taken off life support on Wednesday after his family made the decision to donate his organs.

LISTEN: WBBM Newsradio’s Bernie Tafoya reports

As WBBM Newsradio’s Bernie Tafoya reports, police are searching for two brothers, ages 26 and 28. Because they are only wanted for questioning and have not been charged with any crime, their names are not being made public.

But police say they may be driving an older-model white Cadillac STS with Illinois license plates.

Meanwhile, Antonio – an honor roll student at Marshall High School – continues to live on, in a way. That’s because, as CBS 2′s Mike Puccinelli reports, Antonio’s organs were donated to as many as five other people.

Illinois Secretary of State Jesse White, a longtime proponent of the state’s organ donor registry, offered his condolences Thursday to R.C. Wardlow, a longtime friend and colleague in his office and Antonio’s grandfather.

“He wanted to be a lawyer,” Wardlow said of his grandson. But Antonio never had a chance to do that, because he was gunned down on his front steps on Sunday.

Wardlow received the news by phone.

“I got a call from my son Donny and I didn’t recognize the voice because he was hysterical, crying,” Wardlow said.

Antonio had been shot in the head. His mother, who was also sitting on the front steps, was shot in the arm. She survived the drive-by shooting, her son did not.

“He was just a joyful person – nothing negative, nothing negative – just a sweet person,” Wardlow said.

Upon learning recently of his grandmother’s dire need of a kidney transplant, Antonio had offered up his own. His mother refused to allow him to make the donation because he wouldn’t be able to keep playing football, but Wardlow said the offer exemplified Antonio’s generous spirit.

“Anytime you’re a 15-year-old and your grandmother need a kidney and you step forward and say ‘It’s okay grandma, I’ll give you this kidney,’ … that speak many words of him, his kindness,” Wardlow said.

So when Antonio was taken off life support and died on Wednesday, his family made the decision to donate his organs so that others might live. His grandmother got the kidney transplant and four other people also received organs from Antonio.

“A fifteen year old in Arkansas was given the heart, his grandmother got the kidney and two or three other people got the lungs and the eyes,” Wardlow said.

Antonio’s grandmother also had been shot several years ago and was paralyzed.

White said, “When you can give someone else a second chance in life, you fall into the category of being a hero. And Antonio is a hero.”

Antonio has become a hero who inspired his grandfather in life.

“He inspired me to step forward and be (an organ) donor. If this hadn’t have happened, I probably would never have came up to that, you know, never thought about that,” Wardlow said.

White said that his own sister’s life was saved when she received a donated kidney, but he said there are 5,000 people in Illinois currently waiting for organs. Each year, 300 of those folks die waiting, so the need is great.