The mother of a Canadian killed while fighting Islamic State militants in Syria said her heart was heavy as she put her hands on a casket containing the body of her son.

Tina Martino of Niagara Falls says she has not yet been able to see the remains of her 24-year-old son, Nazzareno Tassone, because his casket was sealed when it arrived in Canada late Saturday months after his death.

"As I lay my hands on the casket, sadness came over me," Martino said Sunday. "I'm still wondering, 'Is this my boy?'"

Tassone was killed on Dec. 21 in the city of Raqqa while fighting militants associated with the Islamic State of Iraq and the Levant, known as ISIL.

The young man had told his family that he was going to Iraq to teach English, but he secretly slipped into Syria to join forces with a U.S.-backed Kurdish group called the YPG.

The YPG told Tassone's family that his body was taken by ISIL militants, and wasn't recovered until May.

Martino said she still has doubts about the identity of the person in the casket because of a presumed error in an initial autopsy report she was sent — it listed her son as having a different hair colour, being several inches taller than he was and more than a decade older.

Officials said they later confirmed the body was Tassone based on dental records.

But Martino said now that the body is back in Canada, the Office of the Chief Coroner will do another autopsy to verify his identity.

She said they should also be able to determine his cause of death — the autopsy report she received concluded her son died from a blow to the head, not a gunshot wound as she had previously been told.

But the new investigation means Martino won't be able to bury her son right away as she had initially planned, because it's not yet known how long the coroner's autopsy will take.

"They don't know what shape the body is in when they receive it," she said.

Martino said she and her children waited five hours at a warehouse for her son's body to arrive. She said some of her kids had hoped to be able to see the body, but the casket he was transported in was sealed for the investigation.

"A couple of them thought that was actually going to happen, but he goes straight to forensic science," she said.

"I wanted just to be able to bury him this Wednesday. And I just couldn't do it. I couldn't. To be in such doubt," she said.

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She said she hopes the investigation will be finished before July 3, when she is due to return to work.

"So we will sit here one more time and hopefully the team will be quick."