I was being detained in the Cook County Jail in Chicago when my little brother Alex was murdered in the summer of 2005 — shot and killed on the far north side of Chicago. He was just 18 years old.

Tears filled my eyes and my chest tightened when I heard the news. I also felt guilt-ridden. I’d only seen Alex twice in 10 years, the last time when he was 12 years old, and before then when he was 8. In my mind, I could only see him as an 8- or 12-year-old boy succumbing to gunfire.

My family took his death hard. Alex was loved. He smiled often, brought good energy to family gatherings, and was a comfort to siblings and cousins alike.

After the news, I was tortured by self-loathing. Among our siblings, I had been the only gang member — or so I thought. When I heard that Alex was killed because of his gang affiliation, I felt like he had followed in my footsteps.

I wished I could go back and change what happened, but I also felt a deep urge to retaliate. Over and over, scenes played in my head of encountering the person responsible. In jail, I asked people who hung out near where he was killed whether they knew anything about who did it.

Once I learned the name of the person and got a description, my thoughts worsened. Before, I could only imagine a monstrous figure pulling the trigger, but now I had a name and a face.

As the months passed, I began thinking about the killer’s humanity — and about why I shouldn’t retaliate. What if he were the same age as Alex? I was 27 years old. How could I justify committing violence against someone so young? It would not bring Alex back. More importantly, I knew any violent act I undertook would be about me trying to assuage my guilt and nothing more.

One evening, a group of about 10 men moved to my tier. The corrections officer assigned them to their cells by calling out their names and telling them where to go. One of the names made me cringe.

It occurred to me that this may be the person the streets said killed Alex. The next day, my cellmate showed the man my brother’s obituary. He admitted that he was charged with Alex’s death, but he claimed that the authorities had the wrong person.

When my cellie relayed that to me, I was angry again. All I could see was my brother being shot. But a moment later, I saw the young man’s face in my mind too — a 19-year-old human. A scared kid who, by a fluke in the justice system, fell into my world.

In the end, he and I — mediated by my cellie — agreed that he would leave the tier immediately. While I was able to recognize his humanity, I was also in pain and could not trust myself to be in the same detained space as him.

I look back at that moment and see how it was a learning experience. At first, it was an opportunity for me to decide whether to be merciless or merciful. Then, I saw it as an opportunity for him to learn from that mercy. But now, almost 20 years later, I understand that moment was meant to invalidate violence as a legitimate option to seek revenge for someone’s mistake.