Okay, so imagine you're playing a game of "whodunit" with your friends. You're trying to figure out who stole the cookies from the cookie jar. One of your friends, Martin, gets accused of being the thief. But Martin says he didn't do it!
Now, imagine this went on for years, and Martin even got thrown in jail because people thought he did something he didn't do. That's kind of what happened to Martin Tankleff.
When Martin was 17 years old, his parents were attacked in their home and his mother was killed. Martin's father was also hurt, but he survived. The police thought Martin did it, even though he said he didn't.
After a long trial, Martin was found guilty and went to jail for almost 18 years! But then, some new evidence was found that showed Martin was innocent. He went back to court and was finally set free.
So, basically, Martin Tankleff was a guy who got blamed for something he didn't do, went to jail for a long time, but was finally shown to be innocent and set free. It was a big deal because it showed that sometimes the justice system can make mistakes, and it's important to keep looking for the truth even when it seems like we already found it.