SECURITY was tight on Paris trains yesterday, while police investigated a mystery blast last month that may have been a test for Tuesday's bomb which killed three people.
False bomb alerts have disrupted traffic on the Paris underground rail network since the bomb planted by suspected Algerian Islamic guerrillas tore through a train at the Port Royal station.
The blast claimed a third victim when a 25-year-old Moroccan student died of his injuries on Thursday night. Twenty people were still in hospital yesterday out of a total of 94 treated for injuries.
The French Human Rights League called on the authorities not to make the estimated three million Arabs in France scapegoats for the attack.
The head of the Paris regional transport authority said he was studying extra security to seal the areas under seats in trains and buses to make it harder to conceal bombs. Tuesday's bomb, concealed in a 27-lb gas canister, was placed under a seat in a bag.
Mr Jean-Paul Bailly added that it would involve redesigning 200,000 seats in underground, trains.
Investigators, expecting a long and painstaking inquiry, were also looking into an explosion south of Paris on November 19th which they suspect was a test run for the bomb on the rush-hour train. False alarms threw suburban express railway traffic into disarray yesterday.