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He was shot three times at point blank range by a gunman on the run from detectives in Baron's Court, West London.
Within two hours of the killing, a large Victorian house was searched after routine enquiries.
The basement was found to contain enough bomb-making equipment to make half a dozen high explosive bombs as well as a box of ammunition and an automatic pistol.
It is the first IRA bomb factory to be found in London.
Deputy Assistant Commissioner Ernest Bond said: "Evidence shows that the equipment can be definitely connected with other bomb incidents and outrages recently in London and the provinces."
Four men are registered as tenants.
Shot in the chest
No-one has been arrested at the flat but police have rounded up 18 Irish men and have applied to detain further at least six of those under the provisions of the anti-terrorism act passed last year.
Yesterday, a plain-clothes detective patrolling Charleville Rd and Fairholme Rd, where the "bomb factory" was later found, saw a man acting suspiciously and questioned him.
He ran off and the detective and two other officers gave chase.
PC Tibble was passing by on his motorbike and although he was off duty he rode after the suspect and overtook him.
He then got off his bike and stood in front of the fugitive with arms stretched out, at which point the man shot him three times in the chest.
The Royal Ulster Constabulary is helping Scotland Yard in the hunt for the killer.
There has been an overwhelming response from the public and donations offered for PC Tibble's widow.
In Context:
Liam Quinn, Stephen Tibble's killer, escaped to San Francisco.
He lost a 13-year battle against extradition from the United States and returned to Britain to face trial.
He was jailed for life in 1988 with a recommended minimum sentence of 30 years.
As part of a deal with Sinn Fein under the Good Friday Agreement, he was freed from the high-security Portaloise Prison 11 years later in April 1999, much to the horror of police officers in England and Northern Ireland.
The four men with whom he was associated - known as the Balcombe Street Gang - were released at the same time.
They had carried out a series of bombings on the mainland and murdered co-founder of the Guinness Book of Records Ross McWhirter and Gordon Hamilton-Fairley, one of the world's leading cancer specialists.
"The wicked flee when no man pursueth but the righteous are bold as a lion"
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