At a desk within the D.C. police homicide unit, a lone photo of a smiling, baby-toothed, slightly dimpled-cheeked baby boy is tacked to a partition.

It shows Carmelo Duncan celebrating his first birthday just months before he was fatally shot, the youngest victim of deadly gun violence in the District last year.

On a December night, at least two people fired at Carmelo’s father’s car as he drove down Southern Avenue in Southeast Washington, police have said. Carmelo was hit several times, including in the head.

No arrests have been made in the Dec. 2 shooting that shocked the nation’s capital. And for the three D.C. homicide detectives who investigate the deaths of the city’s youngest victims, Carmelo’s case remains as vivid as if it happened yesterday.

“He’s a complete innocent,” said Detective Chanel Howard, who pinned Carmelo’s photo at her desk.“He may be our youngest ever. And I want to remember him. I want to make sure I do my best by him. There is just no explanation for this.”

Howard and her colleagues, Gus Giannakoulias and Anthony D. Greene, along with a supervisor, make up the D.C. police Special Victims Unit, the division that investigates injuries and deaths of children ages 12 and younger.

Last year, the unit investigated three cases involving children killed by gunfire. That was the most, the detectives said, in recent memory. The city saw one child fatally shot in 2018 and one in 2019. In 2017 and 2016, there were none.

The trio, led by their sergeant, are among the most senior D.C. police homicide detectives. And although all homicide investigations are difficult, cases involving children can be the most emotionally challenging.

“We take it very personally to do our best to investigate these cases thoroughly to bring justice to the families,” Giannakoulias said. “I could not imagine ever losing a child. Especially a child to violence.”

Giannakoulias, 55, (pronounced Yi-na-kou-las) is the most senior of the three. He joined the D.C. police in 1990 and moved to the unit in 2018. He was the lead detective in the 2018 fatal shooting of 10-year-old Makiyah Wilson. One July afternoon as Makiyah was walking to an ice cream truck in her Northeast Washington neighborhood, she was caught in a hail of bullets fired by rival street gangs, police said. Nine people were arrested and are awaiting trial.

Howard, 50, has been with the department for 22 years. She joined the SVU last year after years investigating homicides. Howard led the probe into the 2013 fatal shooting of a Southwest man by his wife, then a Walter Reed pharmacist, who claimed self-defense. Following the 2019 trial, a jury convicted her of voluntary manslaughter. She was sentenced to nearly eight years in prison.

Greene, 47, joined the force in 1994. After working his way up to the homicide branch, he joined the SVU in 2016. He investigated last year’s fatal shooting of 11-year-old Davon McNeal, killed by a stray bullet during a Fourth of July anti-violence cookout in Southeast. Four people were arrested in connection with his killing and are awaiting trial.

Davon’s mother, Crystal McNeal,said she was initially apprehensive about Greene. She had never had any dealings with police officers and had been warned by family and friends not to trust officers, whom they saw as “nasty” and “uncaring.”

But Greene was “totally different,” she said. “You could tell he was hurt about this, too. He kept me posted about everything.”

In the long days following the shooting, McNeal recalled how Greene sat next to her, looked in her eyes and promised he would find her son’s killer. “He did what he said he was going to do. They caught every last one of the guys,” she said.

In addition to Carmelo and Davon, Malachi Lukes also was fatally shot last year. The 13-year-old was struck in the neck one Sunday afternoon last March as he was walking with friends to a basketball court in Northwest Washington. Giannakoulias was instructed to handle the case even though Malachi was older than 12. Four alleged neighborhood gang members were eventually arrested in the killings. Their cases are pending in court.

One recent afternoon as the detectives discussed the slayings, their voices filled with anger and frustration.

“I’ve seen multiple shootings in the past. But to see someone that young. . .” Greene said, his voice trailing off, “it does something to you. I can’t even describe it.”

Individuals armed with rage and a firearm no longer care whom they injure or kill in their desire to settle a score, the detectives say. Greene, a District native, recalled how decades ago, there seemed to be an unspoken code in the city that if an intended victim was in proximity of a woman or child, the attacker would wait. “Women and children were off limits. But now, we’re seeing so many children and women murdered in this city. I don’t understand this disconnect. Or maybe they just don’t care,” he said.

Fueling the deaths, the detectives say, is an increased number of guns on city streets, including assault rifles, such as those used in Makiyah’s shooting. Children can be unintended victims when the weapons are used to settle disputes.

“The amount of firepower that they have in this city is unbelievable,” Giannakoulias said. “Back in the day, you would never see an assault rifle on a homicide scene. Now it’s commonplace. We are lucky that we haven’t had multiple children on scenes dead.”

The detectives also investigate other child deaths, including suspected beatings from parents or guardians. They said the majority of the deaths they see are infants who were accidentally smothered when co-sleeping with their parents.

Like dozens of cases scheduled to go to trial last year, the trial in Makiyah’s killing was delayed because of the pandemic. Makiyah’s mother, Donnetta Wilson, said “Detective Gus,” as she calls him, has been regularly updating her on the status of the case. “Even when this happened, he was right there for me, taking the time to tell me everything. He made me feel like he was heartbroken about what happened,” Wilson said.

Carmelo’s mother did not return calls for comment.

In his case, the detectives remain frustrated. In the days after the shooting, about a dozen anonymous tips came in, the detectives said. They believe more people have information.

In addition to suspects, the detectives are trying to identify a motive. Did anyone hold animosity toward someone in Carmelo’s family? Or was the car mistaken for someone else’s?

“His life was snuffed out. This bothers us. It bothers us greatly,” Giannakoulias said of Carmelo. “This child had a future. He could have been the president 40 years from now. But the person or people responsible took that away from him.”

There can be a variety of reasons, these seasoned detectives say, that residents don’t cooperate with police, even anonymously. Some are afraid of retaliation from the suspects, although the detectives said they can protect their witnesses. In other cases, people want to seek out justice on their own, which often means additional violence.

One of the most common reasons for lack of cooperation, the detectives acknowledge, is a lack of trust in police among many city residents. The detectives say they understand these concerns, but still need the public’s help to hold killers accountable.

“This has to bother somebody out there,” Greene said. “We can’t do this without the public. This isn’t TV where a case is solved in an hour. This is real life.”

There also are people, Howard said, who have information but opt to hold on to it in exchange for leniency should they one day get arrested in their own case.

“Carmelo is not a bargaining chip. This is not that case,” Howard said. “It’s going to come out. People around you noticed your behavior changed and suspected you did something. But instead, you didn’t say something and you allowed the death of a 1-year-old to go unanswered for.”

The reward for information in Carmelo’s death remains at $60,000. D.C. police fliers were distributed with the unit’s phone number: 202-645-9600.

“We will find the perpetrator of this. There is no doubt in my mind,” Giannakoulias said. “You’re not going to kill a 1-year-old in this city and think you’re going to get away with it.”