'They had him. They had the weapon.' Five years after her brother's murder, one Chicago woman surprisingly learns justice will never come.

CHICAGO (CBS) -- 2017 was a cruel year for Tina Lyles. That June, she said, "Someone called me and told me something had happened to Quinton," Quinton Flowers was her 19-year-old son. He was an aspiring musician. She adopted him when he was just 4 years old.

That day in 2017 she got a phone call and learned he had been shot, not far from home. "One of our neighbors performed CPR and brought him back," she described what happened through tears.

Tina said goodbye to Quinton soon after that phone call in the hospital. "He had a horrified look on his face, that I never have seen. He looked horrified. We all told him that we loved him and then we let him go."

As the following days grew into weeks and months – Tina had to stay strong to keep her family together. Quinton and his older brother, Moncreef Miller were close, she said. "Quinton gave Moncreef an opportunity to be a big brother. He hadn't been a big brother ever, being the youngest of my biological kids."

That's why Quinton's murder hit Moncreef especially hard. "It really did something to him; it broke something in him. All the rest of the [family], had eight kids at the time, were pretty torn up."

A few months later, Moncreef became a dad. "This is Moncreef in the hospital when he saw his baby for the first time. Had a big smile."

Shortly after the birth of his daughter, Moncreef was also shot and killed, a few blocks from where Quinton was gunned down. Another devastating loss for Tina. "I said, no, not again. You gotta be kidding me. Not again. "

That's two sons Tina lost to gun violence within six months of each other.

But the brothers were just two of the 660 homicides in Chicago that year.

Arrest rates have varied over the years since Quinton and Moncreef were shot and killed – from a low of 20% in 2017 to a high of 37% so far this year.

That means there are still many more mothers like Tina out there wondering when a killer will be caught. Over the years, she tried to stay in touch with police, "If we find out anything, we'll give you a call. I never got a call."

She has turned to therapy to help with the pain and loss, to a group called Chicago Survivors. The nonprofit provides counseling and support services to families of homicide victims. It also provides training to agencies that deal with victims' relatives such as law enforcement, medical examiner, and hospital staff to respond to families with more compassion.

JaShawn Hill is Director of Clinical Services for Chicago Survivors. She's well aware of Chicago's low arrest rate, "Which sends a message to the community that if you harm somebody with violence, especially homicide, you get away with murder."

Are people getting away with murder in Chicago? Tracking the answer is more puzzling than you might think because making an arrest is only one way the Chicago Police Department (CPD) says they're finished investigating a crime.

In 2021, the arrest rate for homicides was just 24%, but the clearance rate – or the percent of cases CPD closes – was 48%.

How is that possible? It's something called exceptional means. Police take credit for clearing cases even though justice for families is never served.

The same year that Quinton and Moncreef were killed (2017), Anna Villada and her 15-year-old brother, Diego were walking down their Hermosa neighborhood alley to get lunch. Two men jumped them. "One of the dudes told Diego 'Start running because this is the day that you die.'"

Anna said Diego tried to get away but was shot in the head. "He ended up getting shot over there, but his killer was standing on that end," she said as she pointed to opposite directions in the alley.

Anna said she got a good look at the killer and described him to police. Then, she joined her family at the hospital to say goodbye. "I told him you can't leave me. You really can't leave me. You can't leave me by myself. I get close to his face, and I tell him, if you want to go just go, I know you're in pain. I don't want to see you suffer like this. His machine started going off and I see tears coming down. So I told him, okay. I'm fine. I'll let you go."

Diego Villada died at the hospital two days after he was shot. Sitting by her brother's bedside, Anna felt like an arrest would come soon. "First in my head, was like, yeah, he's gonna get justice. They have him. They have the weapon."

Police did make an arrest in Diego's case. But, according to CPD records, this case was cleared in 2021. It was one of those exceptional cases because prosecutors declined to charge the suspect.

Failure to file charges is just one way CPD closes cases. They also consider the crime solved when the prime suspect is in jail in another jurisdiction for something else and can't be extradited. Also, when the prime suspect is dead, or police are unable to uncover enough evidence. Sometimes cases are closed when police arrest the wrong person.

More troubling CBS News' data analysis shows this method is actually increasing. In Chicago, between 2017 and 2021, cases cleared exceptionally with no charges grew from 37% to 51%. More than half of all of the closed cases.

Loyola University Criminal Justice Professor Arthur Lurigio says arrest is only the first step in solving a crime and a lack of accountability perpetuates the cycle.

"That's a critical mass of survivors of homicide victims that are never going to experience the justice that they deserve," he said.

For Anna and her family, it gets worse. They never knew Diego's case was closed until we told them. She said it doesn't feel like justice. "They just told us the same thing over and over. We'll get back to you in a couple of weeks. We'll get back to you. We'll get back to you. His case is still open. We have everything we need. And for them to not even give us one phone call to tell us the case is closed. It's sad."

The Cook County State's Attorney's Office (SAO) told the CBS 2 Investigators charges were rejected in Diego's murder in 2021 because of a lack of evidence to prosecute.

Why are more cases like Diego Villada's being closed exceptionally? Why are fewer cases like Tina Lyles' sons being solved with an arrest? We asked for sit-down interviews with both the SAO and CPD. Both refused. Instead, they pointed fingers at each other.

"There is something seriously broken and not just in this society, but with the system, the justice system," said Tina Lyles.

Leaving families waiting for closure they'll never get.

"My mom comes up to me and she hugged me. And she asked me what are we going to do now," said Anna Villada.

CPD pointed out that homicide arrests are up so far in 2022. The department said smart policing technology has benefited their investigations, but ultimately charging decisions are up to the SAO. The SAO said if there's enough evidence to approve charges then they do.

What we found in Chicago is part of a CBS News Investigation into the reasons for unsolved murders across the country. This graph shows national homicide clearance rates.

Complete coverage of "Crime Without Punishment' from our CBS stations across the country and CBS News is available here.