The man who committed the brazen attack on Parliament Hill that left a Canadian soldier dead was driven by a political and ideological motive, the RCMP said, as it provided new details that shed light on the assault that shook Ottawa last week.

Michael Zehaf-Bibeau prepared a video shortly before he shot a Canadian soldier at the National War Memorial and stormed Parliament, according to police. The video is being analyzed by the RCMP and will not be immediately released. But RCMP Commissioner Bob Paulson said in a statement that police had uncovered "persuasive evidence" of Mr. Zehaf-Bibeau's motivation.

The news came a day after Mr. Zehaf-Bibeau's mother said in a letter that he told her he intended to travel to Saudi Arabia, not Syria, had he been able to acquire a passport, to study the Koran. The RCMP told the public that Mr. Zehaf-Bibeau was seeking to travel to Syria, which they wrongly attributed to his mother, Susan Bibeau. In a letter published this weekend, she said she doesn't believe he was part of an organization or "some grand ideology," and that he acted "out of despair."

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The interwoven questions of whether Mr. Zehaf-Bibeau was mentally ill, whether he was ideologically motivated, whether he thought he was acting on behalf of the Islamic State and whether he moved on his own will take on added significance this week as the Conservative government is expected to table legislation that would enhance the power of intelligence agencies.

Reached by The Globe and Mail Sunday night, Commissioner Paulson said that the video was a short one in which Mr. Zehaf-Bibeau appeared "lucid and purposeful."

He said the RCMP cannot release the video or give further details about it at this time. "It may be evidence," he said. Still, Mr. Paulson said, the public should know about its existence. "There's no agenda to putting it out," he said. The RCMP statement provided details that illuminate some aspects of the attack, including how an apparently homeless, drug-addicted drifter was able to fund his assault.

Mr. Zehaf-Bibeau had worked in the Alberta oil sands and had amassed a considerable sum of money, the RCMP said. That helps explain how he was able to purchase a used car that he drove up to Parliament Hill before hijacking a minister's car. The police said they continue to investigate how Mr. Zehaf-Bibeau distributed the rest of that money prior to his killing.

The question of how Mr. Zehaf-Bibeau acquired a gun remains under investigation, they said. He was prohibited from possessing weapons due to previous criminal convictions, but the RCMP said they believe the knife he was carrying during the attack was retrieved from an aunt's property in Mont Tremblant, where he had lived years earlier. Investigators are looking into the possibility that the weapon used to kill Corporal Nathan Cirillo at the National War Memorial, a .30-30 Winchester lever action rifle, might have been similarly hidden on the property. They called it an "old and uncommon" gun.

One eyewitness says that Mr. Zehaf-Bibeau shouted the words "For Iraq!" after he shot at the soldier at the National War Memorial.

" He lifted his rifle… his scarf had fallen down. And he just – not much expression on his face – yelled what I heard was 'For Iraq!'" said Hayden Trenholm.

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The political staffer had chanced upon the crime scene as he walked to his job as a policy adviser in a Liberal Senator's office.

He added that "my impression at the time was it was something he was doing because it was a script he had made up for himself."

"The RCMP is also investigating Zehaf-Bibeau's interactions with numerous individuals in the days leading up to this attack," Mr. Paulson said in the statement. "The investigation is focusing on whether these interactions could have contributed or facilitated, in any way, the terrorist attack subsequently committed by Zehaf-Bibeau."

In her letter, Ms. Bibeau said the RCMP got it wrong about her son's intended destination, something she said she brought to their attention and wondered if they had publicly corrected. She said she believed her son felt trapped because his application for a passport had been held up, which frustrated him to the point that he "wanted death." Or he may have wanted to "strike back at the government that had refused him," she wrote in a statement published by Postmedia over the weekend. She said she felt angry and ashamed in the wake of her son's actions, but said he was an unhappy person "at odds with the world." "For me, mental illness is at the centre of this tragedy," she wrote.

The RCMP announced that it had asked the Ontario Provincial Police to take over the investigation into the shooting of Mr. Zehaf-Bibeau, who was brought down by a hail of bullets after bursting through security at a guarded entry to Parliament's Centre Block.

"The RCMP is confident we will have an authoritative and detailed account of the shooting, including a complete reconstruction of the heroic actions of those involved, in the weeks to come," the statement said.