Andrew Michael Crews killed himself seconds after shooting Lori Bowcock at the Peace Arch border crossing south of Vancouver.
CBC News has learned that Crews, 32, last spoke to his mother a few weeks ago, saying he was planning a trip from Seattle back to his boyhood home in Nevada.
Then on Tuesday morning, the Seattle tattoo artist sent his mother a text message, his stepfather, Daniel Lupinek, told CBC News.
"That he loved her, but there was a little message that said, ‘I'm sorry,’” Lupinek said.
Lupinek said Crews moved to Seattle because the tattoo market in Las Vegas was saturated.
His mother and Lupinek spent much of Tuesday trying to contact him after receiving the disturbing message.
"Her first thought was that he was in trouble with the law," said Lupinek.
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Lupinek said the family saw news of the border shooting on the internet, and then Wednesday, they were visited and questioned by U.S. Homeland Security officials.
He said Crews loved music and art, and the main concern of the gunman’s mother now is for her son's soul and the recovery of his victim, Lori Bowcock.
"[Crews’s mother] was deeply concerned about her and her health, that she was very sorry that she was even involved with it."
Bowcock is expected to make a full recovery.
The Peace Arch border crossing – third busiest in the country – was opened to southbound traffic into the U.S. Wednesday afternoon after it was closed for more than 26 hours following the shooting.
Northbound traffic reopen shortly after 8 a.m. PT Thursday.