A lengthy investigation by South London Press reporter Richard Porritt has revealed that the same gun was used in two separate murders just 27 hours apart.
The killer — or killers — linked to his investigation have never been caught, and police say the evidence could spark new lines of enquiry.
Porritt worked closely with an undercover police officer to discover the new evidence in a murder case which has gone unsolved for five years.
Jan Aylward and Steven McCalla were both gunned down in 2001 after being caught up in a South London turf war.
Aylward is thought to have been mistaken for a gangland rival of the killer, but was actually a popular pet shop owner in Streatham.
The results of Porritt's investigation made the SLP's front page on Friday.
He said: "An excellent source came to us with this information that had never been made public before. After a bit more digging we managed to get the information confirmed.
"Family members were willing to talk to me and are now hopeful their son's killer could be brought to justice.
"The new information gave us the chance to run the copy on the front and over two pages inside. That allowed me the space to go in to great detail about what actually happened on the night Jan was killed. This is exactly the type of story I love getting involved with and I am already cracking on with the next."
Porritt joined the SLP from The Huddersfield Daily Examiner, where he was recruited as investigations reporter.