Gerry Tobin was shot in the back of the head

Detectives looking into Sunday's death of Gerry Tobin, 35, in Warwickshire have made "some significant progress".

But Det Supt Ken Lawrence, who is leading the probe, said more peripheral Hells Angels may seek revenge.

Mr Tobin's girlfriend, Rebecca Smith, from south-east London, said his death left a hole "that can never be filled".

A hole that can never be filled has been left in the lives and hearts of so many... Gerry was my life Rebecca Smith

Mr Tobin was shot in the back of the head as he rode home from the Bulldog Bash biker festival, held at Long Marston Airfield, near Stratford-upon-Avon.

Det Supt Lawrence said he would be "astonished" if the murder had been carried out by another Hells Angel because of the code of loyalty within the organisation.

He said it "would be foolish" not to consider there may be retaliation but said he was sure the core membership of the Hells Angels would abide by their principles.

Det Supt Lawrence said: "I don't think this was a plain and simple random attack. There must have been some precursor event.

Two shots

"It's possible he was targeted either specifically because of something he had done or some disagreement that he had had.

"It's not impossible that he was targeted simply because he was a Hells Angel."

Police said there was no obvious motive. They believe at least two shots were fired at Mr Tobin, although only one struck him.

Police described Mr Tobin as a "hard-working, friendly but private person" and was an active church member when he was younger and still living in Canada.

Rebecca Smith feels "truly blessed" to have spent five years with him

He lived with Ms Smith near a Harley-Davidson dealership where he worked as a mechanic in Mottingham.

In a statement, Ms Smith, 25, said: "I would like to take this opportunity to express my thanks and love to all that have supported me and our club at this awful time.

"Thank you to all for your kind words, respects, sentiments and tributes.

"A hole that can never be filled has been left in the lives and hearts of so many. Gerry was my life."

A statement read out by the London Chapter of the Hells Angels on behalf of her said: "To those who knew him, Gerry stood out in the crowd as a true gentleman.

"(His) charming personality (and) quick-witted humour always kept everyone smiling.

"He was Rebecca's soul mate and she feels truly blessed to have spent five wonderful years of her life - the best five years of her life - with such a wonderful man."

Memorial fund

The Canadian had been riding alongside two friends on his Harley-Davidson FXSTB 1500 Night Train after leaving the Bulldog Bash when he was shot dead.

Police said they now believed the green Rover 620 seen near the incident contained at least two and possibly three occupants.

CCTV images have been located from a number of places and forensic evidence from the motorway is being examined.

Warwickshire Police have received more than 300 calls from people in the UK and abroad about the case.

They said the inquiry had some help from bikers' organisations but the response of the Hells Angels had been less than completely open.

The London Hells Angels have set up a memorial fund for Mr Tobin and their website has been deluged with messages from around the world.

A biker event planned for next month, the Chop and Rod show at Henfold Lakes, in Surrey, has been postponed as a result of the shooting.