LONDON - Police arrested three more suspects Wednesday in the slaying of a Canadian biker gunned down while riding his motorcycle on a British freeway.

Gerry Michael Tobin, 35, a former Calgary resident, was shot in the head in August as he returned home from a bikers' festival in central England.

Three men -- aged 44, 45 and 52 -- were detained early Wednesday, a Warwickshire Police spokesman said.

He gave no further details about the suspects, who have not been formally charged.

Four other men were arrested earlier in the slaying, for which the motive remains unclear.

Simon Turner, 40; Dane Garside, 41; and Sean Creighton, 43, have been charged with murder. Dean Taylor, 45, was charged with a firearms offence. All four are due to enter pleas at Birmingham Crown Court on Nov. 26. Police said two vehicles, a firearm and other weapons were seized during a search of properties after the earlier arrests.

Tobin was born in England but moved to Canada when he was a little boy. He moved back to England 10 years ago.