OTTAWA -- An American historian thinks it's possible that German agents touched off the fire which destroyed the Centre Block of Parliament in 1916, in the middle of the First World War.

Heribert von Feilitzsch has spent countless hours piecing together the covert activities of German agents working in the United States during the war -- including plots against Canada.

The historian and businessman hit a gold mine when he found 68 boxes of old financial files at the U.S. National Archives, records of people the Germans paid to carry out sabotage missions around North America.

Was Canada's Parliament one of those targets? The 100th anniversary of the devastating fire was marked Wednesday in the House of Commons, with the reading of the names of the seven people who died in the blaze.

Von Feilitzsch hasn't come up with a definitive answer as to whether German saboteurs were responsible. But he points out that two other major plots on Canada were planned and the descriptions of the fire itself still hold valuable clues.

"There's a lot of circumstantial evidence and if we could link that to the profile of a pencil-bomb attack, then it would be a pretty tight story," he said from Amissville, Virginia.

A pencil bomb was a cigar-sized, lead cylinder which held two chemical compounds separated by a copper disc. The two compounds would eat away at the disc and burst into flame when they met. A saboteur could time the moment of the attack by adjusting the thickness of the disc.

Such bombs were used by German agents throughout the war, including at a major fire on the Black Tom Island munitions depot in New York harbour in the summer of 1916. The United States would declare war against Germany a year later.

The fire that broke out in the reading room of the Centre Block in 1916 began on a desk shelf. MP Francis Glass, who discovered the fire, said afterwards he didn't smell smoke initially, but noticed a sudden feeling of heat. He called for a caretaker to bring an extinguisher.

"As I could see it, he had not even time to operate it, for the instant he held it in position he was shot back -- the flame enveloped him," Glass told an inquiry.

"(The smoke) was bright red -- I took it for fire -- in fact my impression was it seemed as if the smoke turned to fire almost instantly."

Of course, the reading room was also filled with newspapers and MPs and visitors often ignored the rule not to smoke there. The room's ventilation and its oiled pine walls also helped spread the flames.

But von Feilitzsch, author of the book "The Secret War on the United States in 1915," notes that during the war there was a standing order to attack Canada.

"That order was known to many Germans even along the border and so forth. The Germans were recruiting German-Americans and German-Canadians to do that," he said.

"That order is well known, to blow up installations in Canada."

Records and interviews from the time have revealed that two co-ordinated plots had been planned by German agents in the U.S. -- one on the Welland Canal, and another around the Valcartier military base near Quebec City. Neither mission actually materialized.

Capt. Hans Boehm and Alfred Fritzen had been assigned to the northern border of the United States and were involved in the abandoned Canadian plots. Boehm, a top agent, disappeared back to Germany in February 1916.

"Both of them were dispatched to Canada before, both of them were active in February, both of them had connections and money from the intelligence department of the German army in New York," said Von Feilitzsch.

The rebuilt Centre Block re-opened four years later in 1920. The inquiry set up to find answers about the fire never came to any firm conclusion.

"Wouldn't that be nice to find out exactly what happened?" said von Feilitzsch. "It's a hundred-year-old riddle."