(CNN) -- Robert Zimmerman Jr., the brother of the man who shot and killed 17-year-old Trayvon Martin, apologized for his controversial and offensive tweets. 

In one, Zimmerman juxtaposed a photograph of Martin with one of 17-year-old De'Marquise Elkins, one of two teenagers charged with killing a baby in Georgia. 

Both Elkins and Martin appear to be flipping off the camera. 

"A picture speaks a thousand words. Any questions?" the tweet reads. 

In another tweet, Zimmerman writes: "Lib media shld ask if what these2 black teens did 2 a woman&baby is the reason ppl think blacks mightB risky." 

Speaking on CNN's Piers Morgan Live on Wednesday night, he apologized for the messages, saying they weren't the "right thing to do." 

"I realize those were controversial and offensive and I did publicly apologize for them," he said. "I'm a human being. I'm being upfront about what I did. I made a mistake ... Unfortunately (it) may not have helped George." 

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His brother, George Zimmerman, has been charged with second-degree murder. Zimmerman acknowledged shooting Martin but said it was in self-defense. Attorneys for Martin's family have accused Zimmerman of racially profiling Martin and shooting him "in cold blood." 

Robert Zimmerman Jr. said he was trying to make a larger point in his tweets about the "media and their honesty in portraying the person who encountered my brother February 26, 2012. 

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"We've been led to believe that it's a junior-high-school-aged person because of the pictures," he said, referring to Martin. 
What happened to him?
Robert Zimmerman Jr., the brother of the man who shot and killed 17-year-old Trayvon Martin, apologized for his controversial and offensive tweets. 