It was the first homicide of the summer, breaking the longest stretch without a slaying in the city in nearly three years.
The prosecutor's office spokesman declined to comment on a possible shooting motive or suspects, citing the active investigation.
Rivera worked for his family, managing a furniture store and a Hispanic food store they own in Camden, friends said. They described a man who had a good heart and loved his family.
"Sergio was a good, quiet, loving person," said Angel Cordero, a community activist in Camden who said he had known Rivera for several years. "It's just a devastating loss."
Rivera participated in three of five recent antiviolence marches that Cordero helped organize, he said.
When a boy went missing a year ago, Cordero said, Rivera organized friends and family to search for him. Rivera ultimately found the boy walking in Cherry Hill and drove him back to the boy's mother, Cordero said.
"Sergio put everybody that he knew out on the streets looking for this kid," Cordero said. "He used all the resources he had."
Rivera had had trouble with the law before. He was convicted in 2002 of possession with intent to distribute a controlled substance. More recently, he made headlines after he shot his 2-year-old son, Joshua, on Dec. 31, 2013, while they were sitting in a car with the boy's mother and grandmother.
Rivera told police that the shooting was accidental; Cordero described it Friday as "a freak accident." Rivera drove the boy to Cooper University Hospital, where he was treated.
Rivera was charged with aggravated assault, unlawful possession of a weapon, and related charges. He was also in possession of oxycodone, according to court records.
Rivera has two sons with his wife, whom he married about five years ago, said Norka "Cary" Soldevila, a longtime family friend. Rivera was also raising a son his wife had from a previous relationship, Soldevila said.
He was scheduled to have a pretrial conference Aug. 11 regarding his son's shooting.
Soldevila said Rivera, with whom she had grown up in Camden, was a huge sports fan, playing on a recreational baseball team and bowling team. He also helped coach baseball, especially as his sons became interested in the sport, she said.
Rivera had enjoyed baseball since he was a young boy, Soldevila said, and he often played sports with her brothers. She said he was also an avid Philadelphia Eagles fan.
Soldevila said she learned of Rivera's shooting around 3 a.m. Friday when a mutual friend called her. She went to the home, where police tape kept her at bay while detectives were investigating the scene. At the hospital, she learned that he had been killed.
It has been a difficult few months for Soldevila, who just lost her 22-year-old son, Ernesto Torres, in a violent crime. Torres was shot and killed in Camden on April 3.
"It's very sad that his family has to go through this, that his mother has to go through this. I just lost my son, I know what losing my child is: devastating," Soldevila said.
In Camden, the summer season has historically been marked by a higher frequency of slayings. Rivera is the 19th reported homicide victim in the city this year. The most recent death prior to Rivera's involved Giovanni DeGregorio, 31, who was gunned down in Fairview on June 8.
The 40 days between the killings of DeGregorio and Rivera was the longest period of time without a homicide in Camden since a 42-day stretch in September 2011.
"It's remarkable progression on one hand and a stark reminder that we still have plenty of work to do in changing the culture of violence, on the other hand," Scott Thomson, chief of the Camden County Police Department, said in an e-mail.
One Camden resident who has experienced the worst of this culture is Soldevila, who struggled Friday to express herself. Rivera had tried to help keep her son out of trouble, she said, and having the two killings come within months of each other has hit her hard.
"No words. I'm lost for words. We just pray. What is there to do? What can we do?" Soldevila said. "Be here for each other. I feel as though our family is our strength. As long as we stay together - I mean, it's really hard - but we get through it by sticking together."