Koy Bentley was fatally wounded on the fifth floor of a block of flats in Watford on Monday afternoon.
Hertfordshire police initially said the death was "suspicious". No arrests have yet been made.
Det Insp Pushpa Guild said: "Extensive inquiries are continuing at this time to establish the exact circumstances surrounding Koy's death."
An appeal for information has been launched.

It was hoped the size of the clothing optional section of coastline in Budleigh Salterton, Devon, would be increased after tidal activity rendered the current area "uncomfortable" to sit on.
But the town council blocked the move.
British Naturism said the decision was "ridiculous" and "offensive" to its members.
The council was unconvinced by the argument the tide had washed away pebbles on the beach and left rock behind, making it "too uncomfortable" for naturists.
Its foreshore and footpaths committee said naturists could still use the beach if they put a "towel or lilo down" and voted against extending it by 200 yards (183m) eastwards.
Andrew Welch, from British Naturism, said: "Naturism is not illegal and we don't need designated places so it is offensive for any social group like ours to be treated in this way.
"It harks back to the 1950s and we want to show these ridiculous authority figures that they are wrong and completely out of touch."
Town mayor Courtney Richards said if the nudist beach was extended it would be about 200 yards from the town's beach huts.
"Budleigh Salterton is a family friendly town and I feel it is something families could do without, so I have a problem with them coming nearer to the town," he said.
"And I think the majority of people in Budleigh Salterton would not want that either."
However, Mr Welch said the council should designate a new beach for naturists.
The closest alternative is Weston Mouth, near Branscombe, about 10 miles away.
East Devon District Council, which owns the beach, has also been asked if the site can be moved but has made no decision.
A spokeswoman said it would work with the town council on the request.
The "nude" section of Budleigh beach was first designated in the 1970s.
The death of a 15-year-old boy found stabbed in the chest is being treated as murder, police have confirmed.
[NEXT_CONCEPT]
Naturists have branded a decision to deny their bid to extend a section of nudist beach as "old-fashioned".