Detective Inspector Nick Barnes led the West Midlands Police murder investigation into the 15-year-old's death.
Keelan was stabbed more than 40 times near his Wolverhampton as part of a feud between the city's V2 and V3 gangs.
Detectives and forensic teams were eventually able to bring charges against four men, who were this week found guilty of his murder after a three-month trial.
"This was a really horrific crime that these four people committed," Det Insp Barnes told the Express & Star.
"I think this crime stood out from any crime that we have dealt with, in the homicide department.
"This is due to two factors really. One was the age of the victim. He was only 15-years-old when this took place.
"Secondly, the level of injuries that he suffered. We know that he suffered over forty injuries as a result of this attack.
"There are very few murders that we have dealt with here where the injuries are that horrific. It really is a stand-out crime in that respect."
Watch CCTV released by police:
It has been a long journey for Keelan's family, who have sought justice since his death on May 29, 2018. He was attacked in a taxi in Merry Hill at around 11pm.
DI Barnes admitted the investigation had been a "difficult and lengthy" one.
It involved sifting through hundreds of pieces CCTV footage and examining multiple mobile phones - including one belonging to killer Nehemie Tampwo, where a rap song glorifying violence and referencing Keelan's name was discovered.
Several people were also arrested as part of the murder probe, but did not have charges brought against them.
The key pieces of evidence, however, were separate bits of DNA which placed Tampwo, Brian Sasa and Zenay Pennant-Phillips at the crime scene.
Tampwo was found in possession of clothing containing Keelan's blood the day after his death, while the DNA of Sasa and Pennant-Phillips were found on a taxi, which Keelan was dragged out of before he was killed on Strathfield Walk.
"Some of the key evidence has been the forensic evidence," said DI Barnes.
"Three of the four were really heavily linked from the start with key, forensic evidence.
"I'm really grateful to the work that colleagues in the forensic world have done to get us that evidence."
While Keelan was just 15 when he was killed, at the time his killers were also just 16 and 17.
During the trial, the court heard that the defendants were linked to postcode gangs.
DI Barnes says there is active work going on between West Midlands Police and schools within the city to prevent youngsters falling into gang culture.
At the time of Keelan's death, he said none of the four defendants were on "police radar as being gang members at that time".
"It was difficult to have prevented this from happening," he said.
The work around schools involves reaching vulnerable children before they got drawn into that lifestyle, which can include carrying knives.
He said this work is extensive but one that is important and must continue in order to "prevent these things from happening in the future".
DI Barnes added: "Our heart goes out to Keelan's family. What happened to him was terrible.
"I know that it has been difficult, with the amount of time that the investigation has taken to get to where it is, which has been difficult for them.
"But hopefully, this verdict gives them some comfort.
"I know Keelan can never be returned to them so our thoughts go out to them."
Sasa, 20, of Long Ley, Heath Town; Tampwo, 20, of Fern Grove, Bletchley; Tyrique King, 19, of Chelwood Gardens, Bilston; and Pennant-Phillips, 19, whose address cannot be published; are due to be sentenced in March.