Forensics specialists yesterday examined the two vehicles, while other officers conducted door-to-door inquiries and searched sewer drains and nearby bushes for spent cartridges and bomb fragments.
Police said they still were not sure how many assailants were involved. The possibility was raised that one IRA member could have been responsible for both attacks, first setting the car bomb in the town of Nieuw Bergen, then driving the short distance to Roermond, where the second incident occurred.
Officials acknowledged the possibility that the assailant or assailants quickly slipped across nearby borders into West Germany or Belgium or vanished into Amsterdam, where the IRA is believed to maintain a number of safe houses.
British Armed Forces Minister Ian Stewart condemned the attacks and urged close cooperation between London and Dublin to beat terrorism. He said security would be stepped up at British bases on the continent to meet any new guerrilla challenge.
All of those killed, and three injured British servicemen, were members of the Royal Air Force and stationed at RAF bases in West Germany. The small Dutch towns in which the incidents occurred are located just across the West German border and are popular social centers for off-duty British military personnel. In both cases, the servicemen had just left nightspots.
The British military in West Germany said yesterday that it was reviewing its policy of requiring that all private automobiles belonging to service personnel carry official British military license plates, a factor that is believed to have made the victims of the attacks readily identifiable to their assailants.
Security at British bases in West Germany was stepped up, and signs at the Dutch border warned military personnel to stay away.
The IRA, which considers itself in a state of war with the British government, has declared all official personnel to be legitimite targets.
Republican sources close to the IRA leadership in Belfast, Northern Ireland, said the attacks were carried out partly as revenge, for the March shooting of three unarmed guerrillas by British forces in Gibraltar and for the jailing of two Republicans in Belfast last week. Witnesses have said that two of the guerrillas inb Gibraltar were trying to surrender when they were killed.
Brendan McFarlane and Gerard Kelly, jailed for five years for leading a jail break in Northern Ireland, had both been extradited from the Netherlands after a long legal battle.
Despite anger over the Gibraltar shootings and a string of incidents that have clouded bilateral relations, the Irish Republic has continued cooperating with London to fight the guerrillas.