There's more to watch on iPlayerpublished at 18:09 British Summer Time 3 April 2023
This case has shone a light on organised crime, drugs and guns on Liverpool, and BBC Panorama has been investigating how they have taken hold in the city.
Reporter Bronagh Munro has spoken to people who used extreme violence to sell drugs, including former gang leader Darren Gee.
"Without violence, you can't deal drugs," said Gee, adding that his gang had been involved in gun crime, knife crime and kidnapping.
He was jailed in 2006 for conspiring to murder someone in a revenge attack.
But he got the wrong man killed.
Watch as he is asked how he feels about the crime now.
You can watch the full Panorama film - The Drug Wars that Killed Olivia – on BBC iplayer now and on BBC One at 20:00 BST (UK).
'Without violence, you can't deal drugs'