An FBI handwriting expert testified at the trial of accused mail bomber Guido Amsel Wednesday, telling a Manitoba court he could not positively identify handwriting found on three bomb packages as belonging to Amsel.

Peter Belcastro said four writing samples seized from three bomb packages — all written in block letters — "may have been prepared by the same writer or writers."

But when he compared those same four writing samples to documents confirmed to contain Amsel's writing, he found both similarities and inconsistencies, leaving him unable to determine whether Amsel was the person who addressed the mail bombs and wrote a note included in one of the packages, he said.

Amsel, 51, faces five counts of attempted murder, one count of aggravated assault and several explosive offences in connection with bombs that were delivered to two Winnipeg law firms on River Avenue and Stradbrook Avenue and to his ex-wife's workplace on Washington Avenue in July 2015, as well as a 2013 explosion at his ex-wife's home.

Lawyer Maria Mitousis, who did some work for Amsel's ex-wife, lost a hand and suffered injuries to her neck, face, chest and thighs when one of the bombs went off in her hands.

'No-conclusion determination': FBI expert

Belcastro said while he couldn't tie the writing on the packages to Amsel, he also couldn't rule him out.

"I was able to reach a no-conclusion determination based on limited clarity and unknown characteristics," said Belcastro, noting his assessment was complicated by the fact he was working from photographs and not originals.

"There was limited uppercase handwriting repeated [in the confirmed Amsel writings] allowing me to make a conclusion either way," he said.

"I can have 100 pages of known handwriting, [but] if I'm comparing it to hand printing, the 100 pages of handwriting means nothing to me."

Belcastro said in an ideal situation, a suspect would be requested to supply investigators with fresh signatures and lengthy writing samples to provide a "meaningful comparison."

Court heard no evidence Amsel provided any handwriting samples to investigators.