I've getting a bit sick of saying why tbh... The only evidence the jury has to make the decision is the testimony of the involved officers (ignoring Witness B) which isn't strong enough to say it was lawful imo, it should've been an open verdict.
Stop saying it then, as it is not true
A quick look at the details of the inquest would have shown you that there were testimonies (some oral, some written) from a broad range of people. A list is below. Some will have been direct witnesses to the actual incident, some to the previous incident when the firearm was passed to Duggan. Others will be indirect witnesses. Others provide medical evidence, forensic evidence or are experts in other fields. The jury will have had ALL THIS EVIDENCE - not just the police vs Witness B you mention - and on the basis of that reached the conclusion that they did.
A/DI Peter SUGGETT: Metropolitan Police Service – DPS Specialist Investigations
Asst Ch Const Stuart CUNDY: Metropolitan Police Service – Trident Gang Crime Command - now Surrey Constabulary
DAC Martin HEWITT: Metropolitan Police Service – ACPO Lead Officer
DC Jonathan PAYNE: Metropolitan Police Service – DPS Specialist Investigations Exhibits
DC Rachael SAMUEL: Metropolitan Police Service – DPS Specialist Investigations Exhibits
DC Steve FAULKNER: Metropolitan Police Service – Lagoon Salon Incident
DCI Steven WILLIAMS: Metropolitan Police Service – DPS Specialist Investigations
DI Brian LUCAS: Metropolitan Police Service – SCD8
DI Katie LILBURN: Metropolitan Police Service – Strategic Firearms Commander
Dr Desmond VANHINSBERGH: Expert Witness – Body Fluids
Dr Michael BARBER: Expert Witness – Fingerprints
Dr Philip SEAMAN: Expert Witness – Ballistics
Dr Simon POOLE: Expert Witness – Pathologist
Dr William GLAZEBROOK: Helicopter Emergency Medical Service Doctor
DS Andrew BELFIELD: Metropolitan Police Service – Lagoon Salon Incident
DS Christopher HANNIGAN: Metropolitan Police Service – Search Team Leader
DS Paul DEMPSEY: Metropolitan Police Service – SCD8 Trident
DSupt Fiona MALLON: Metropolitan Police Service – Strategic Firearms Commander
DSupt Neil EVANS: Metropolitan Police Service – SC&O19 Post Incident Manager (Base)
DSupt Tony NASH: Metropolitan Police Service – SCD8 Trident Post Incident Manager
Insp Brian ELLIOTT: Metropolitan Police Service – Specialist Firearms Operations
Insp Caroline SAUNDERS: Metropolitan Police Service – Borough Duty Officer
Insp Paula MUGGLESTONE: Metropolitan Police Service – PolSA Search Advisor
Inspector U3: Metropolitan Police Service – In Relation to the Anonymous Letter
Miss J: Civilian Witness
Mr Ajaz MIR: Civilian Witness – Employee of Taxi Firm
Mr Andrew BELL: Metropolitan Police Service – Forensic Scientist – blood spatter
Mr Clive BURCHETT: Expert Witness - Imagery
Mr Colin HODGE: Civilian Witness – Vehicle Recovery
Mr Colin SPARROW: Independent Police Complaints Commission – Lead Investigator
Mr Darren BIGGS: Civilian Witness
Mr David BRENNECKE: London Ambulance Service Paramedic and Duty Station Officer
Mr David CUNNINGHAM: Metropolitan Police Service – Forensic Vehicle Pound Officer –
Mr David KIRKPATRICK: Independent Police Complaints Commission – Investigator
Mr Emil DRZEWIECKI: Civilian Witness (with interpreter)
Mr Finbar HANRAHAN: Civilian Witness
Mr Franco TOMEI: Metropolitan Police Service – Forensic Scientist - Ballistics
Mr Gareth JONES: Independent Police Complaints Commission – Investigator
Mr Gary ARKLESS: Metropolitan Police Service – Digital and Electronic Forensic Analyst
Mr Ian RICHARDS: Metropolitan Police Service – Forensic Scientist - Fingerprints
Mr John COCKRAM: Metropolitan Police Service – Crime Scene Manager
Mr John SLAUGHTER: Expert Witness – Toxicology
Mr Jonathan ORFORD: Metropolitan Police Service – Crime Scene Examiner
Mr Kevin HUTCHINSON FOSTER: Civilian witness
Mr Kieran ELY O’CARROLL: Civilian Witness
Mr Luke CLOW: Civilian Witness
Mr Malcolm NOTT: Metropolitan Police Service – Crime Scene Manager
Mr Mark BOWDEN: Expert Witness – Firearms Discharge Residue
Mr Marlon DUGGAN: Brother of Mark Duggan
Mr Michael VAUGHAN: Metropolitan Police Service – Forensic Scientist - Ballistics
Mr Mohammad ASIF: Civilian Witness – Owner of Taxi Firm
Mr Neil JOHNSTONE: Independent Police Complaints Commission – Intelligence Analyst
Mr Nicholas GOLDSMITH: Civilian Witness – Vehicle Recovery
Mr Nino HAMADOUCHE: Civilian Witness
Mr Norman GRODENTZ: Civilian Witness
Mr Paul MARTIN: Metropolitan Police Service – Forensic Vehicle Pound Officer
Mr Richard NOBLE THOMPSON: Civilian Witness
Mr Richard OMOTOSHO: Independent Police Complaints Commission– Investigator
Mr Valentine McGUIRE: Civilian Witness
Mrs Pamela DUGGAN: Mother of Mark Duggan
Ms Angela SHAW: Expert Witness – Firearms Discharge Residue
Ms Anna-Marie O’CONNOR: Expert Witness - Fibres
Ms April BARTER: London Ambulance Service Paramedic
Ms Giedre TILINSKAITE: Civilian Witness
Ms Jacqueline LANDAIS: Metropolitan Police Service – Forensic Scientist - Fingerprints
Ms Nicola HELEY: Independent Police Complaints Commission - Investigator
Ms Patricia LARRIGAN: Metropolitan Police Service – Crime Scene Manager
Ms Saranjeet KHERA: Metropolitan Police Service – Forensic Scientist - DNA
Ms Semone WILSON: Partner of Mark Duggan
Officer A10: National Crime Agency (Serious and Organised Crime Agency)
Officer B17: Metropolitan Police Service – Surveillance Team Leader
Officer B22: Metropolitan Police Service – Surveillance Team
Officer Gary RENNLES: Metropolitan Police Service – SC&O19
Officer Q63: Metropolitan Police Service – SC&O19
Officer R31: Metropolitan Police Service – SC&O19
Officer R68: Metropolitan Police Service – SC&O19
Officer V48: Metropolitan Police Service – SC&O19
Officer V53: Metropolitan Police Service – SC&O19
Officer V59: Metropolitan Police Service – Operational Firearms Commander and Tactical Advisor
Officer W39: Metropolitan Police Service – SC&O19
Officer W42: Metropolitan Police Service – SC&O19 Deputy Team Leader to Officer V59
Officer W42: Metropolitan Police Service – SC&O19 Deputy Team Leader to Officer V59
Officer W56: Metropolitan Police Service – SC&O19
Officer W70: Metropolitan Police Service – SC&O19
Officer Z51: Metropolitan Police Service – Tactical Firearms Commander
Officer ZZ17: Metropolitan Police Service – SCD8 Trident (Bronze briefing)
Officer ZZ37: Metropolitan Police Service – SCD8 Trident (Bronze intelligence)
Officer ZZ46: Metropolitan Police Service – SCD8 Trident (Bronze intelligence)
Officer ZZ50: Metropolitan Police Service – SCD8 Trident
Officer ZZ63: Metropolitan Police Service – SCD8 Trident
Officer ZZ75: Metropolitan Police Service – SCD8 Trident
PC Christopher ALLEN: Metropolitan Police Service – Territorial Support Group
PC Dan GIBSON: Metropolitan Police Service – Armed Response Vehicle Officer
PC Gareth HUGHES: Metropolitan Police Service – Armed Response Vehicle Officer
PC Jim FOWLER: Metropolitan Police Service – Armed Response Vehicle Officer
PC Paul CHRISTIANSEN: Metropolitan Police Service – Armed Response Vehicle Officer –
PC Paul FITZGIBBON: Metropolitan Police Service – Search Team
PC Richard GREEN: Metropolitan Police Service – Armed Response Vehicle Officer
PC Scott NICHOLLS: Metropolitan Police Service – Search Team
PC Steve HARTSHORN: Metropolitan Police Service – Armed Response Vehicle Officer / Police Federation Representative
PC Steven RAINFORD: Metropolitan Police Service – Search Team
Prof Col Jonathan CLASPER: Expert Witness - Surgeon
Prof Derrick POUNDER: Expert Witness - Pathologist
Prof Robert FORREST: Expert Witness – Toxicology
PS Danny WARNER: Metropolitan Police Service – Cordon
PS Stephen BOSWELL: Metropolitan Police Service – Cordon
Supt Shaun DOWE: Metropolitan Police Service – SC&O19 Post Incident Manager (Scene)
T/Supt Mick FOOTE: Metropolitan Police Service – Senior Investigating Officer Op Dibri
T/Supt Simon DOBINSON: Metropolitan Police Service – Chief Firearms Instructor
TAXI DRIVER: Civilian witness (with interpreter)
The Daughter of Miss J: Civilian Witness
V72: Metropolitan Police Service – SC&O19
W39: Metropolitan Police Service – SC&O19
Witness A: Civilian Witness – BBC Video Footage
Witness B: Civilian Witness – BBC Video Footage
Witness C: BBC Journalist
Witness Z: Civilian Witness