By Joseph Akwiri
MOMBASA, Kenya, Sept 24 (Reuters) - A British police officer testified in Kenya on Thursday in the trial of a Briton accused of plotting attacks and who has ties to al Shabaab, the Somali group behind a weekend attack on a Nairobi shopping mall.
Jermaine John Grant, an east Londoner, was arrested in December 2011 in a raid by Kenyan anti-terrorism police on his apartment in the Kenyan port city of Mombasa, along with a female accomplice, Warda Breik, who police said was his wife.
Police said a third suspect, believed to be Briton Samantha Lewthwaite, escaped in that raid.
Witness accounts that there were female attackers in Nairobi mall attack and a comment by a Kenyan minister that a British woman was involved has raised speculation that it was Lewthwaite, branded the "white widow" by the British press.
Lewthwaite is the widow of one of the suicide bombers who killed more than 50 people on London's transport system in 2005.
Grant and Warda face charges of being found in possession of explosive material recovered from their apartment, and a conspiracy to commit a felony, charges they have both denied.
Robert John Garric, a detective constable with Britain's New Scotland Yard police, working in the forensic management team under the counter-terrorism command, told the court he had been part of a team deployed to assist Kenyan police.
Garric said he and his team were told by Kenyan police that "they were looking at a plot to detonate explosives in parts of Kenya." He said he had been informed that a Briton, Grant, had been arrested using a false Canadian identity.
The detectives were led to a government laboratory where they were conducting tests on chemicals recovered from Grant's apartment, Garric said.
Garric, a bomb scene examiner, manager and counter-terrorism investigator, said the kind of chemicals found, if mixed for a short time, could make explosives that "could detonate easily when exposed to shock or flame."
Earlier this month, Grant was acquitted by a Nairobi court of robbery with violence, charges that could have carried the death penalty, but remained in custody because of the trial in Mombasa.
Prosecutor Jacob Ondari said three detectives from Scotland Yard were among his witnesses.
(Editing by Edmund Blair and Ralph Boulton)