Another interviewee said the matrix had left him unable to find work.
"I've applied for so many jobs within the youth sector, and they've told me that when they do like a [Criminal Records Bureau] check, they told me that I'm on a 'watch.' But they don't say exactly what it is," he said.
StopWatch Chief Executive Katrina Ffrench said the gangs matrix leaves targets "marked out for harassment and humiliation," including through stop and search.
"Not only is the matrix completely ineffective at combating the crime it claims to want to tackle, our research suggests it makes crime more likely," she said, according to The Guardian.
Around 3,800 people are currently listed in the gangs matrix, though the Metropolitan police have stated inclusion is always based on at least two confirmed pieces of intelligence.
According to the BBC, a police spokesperson stated the matrix has helped "prevent young lives being lost."
Amnesty International, however, has warned the matrix "routinely" includes individuals with no connection to violent crime. In May, the human rights group issued its own report on the matrix, and concluded the program used "racially discriminatory" practices that overwhelmingly targeted "young black males."
"The entire system is racially discriminatory, stigmatizing young black men for the type of music they listen to or their social media behavior, and perpetuating racial bias with potential impacts in all sorts of areas of their lives," said Kate Allen, Amnesty International U.K.'s director.
People of color are also the main targets of stop and search tactics, according to StopWatch.
"Black people are searched at almost 5 times the rate of whites," the charity found.
The Metropolitan police have previously stated they're working with human rights groups like Amnesty to improve their practices.