James Orr, 84, testified about an email in which Christopher Phillips describes making a box containing osmium tetroxide that could be thrown at police.
Phillips has pleaded not guilty in Nova Scotia Supreme Court to threatening police officers and possessing a weapon — the hazardous chemical osmium tetroxide — for a dangerous purpose.
Orr, a former professor of chemistry at Memorial University, said he had worked with the chemical and described it as a rarity and useful for some reactions.
However, Orr said even when a vial of osmium tetroxide is broken open in a room, it takes time for it to evaporate and begin posing a threat.
"In a normal-sized room I wouldn't expect it (the container with osmium tetroxide) to cause any significant damage ... unless the box hit the person," said Orr.
"I don't see it being anybody's weapon of choice," he said.
Under cross-examination from prosecutor Karen Quigley, Orr conceded that if the osmium tetroxide spilled onto a person or went into their mouth it could be harmful.
Defence lawyer Mike Taylor said outside court that there's been evidence presented that no threat was intended by his client.
The email Phillips sent to a friend in the United States also includes a remark that he wouldn't actually use the container he describes as a weapon.
Phillips also told police in videotaped statements that he intended no harm against police, and that he was using the osmium tetroxide for experimental purposes.
Quigley said the judge will have to consider whether an objective person would regard Phillips's emails and actions as threatening.
"It's not just one piece of evidence. It's all of the actions when one adds them up and weighs them," she said outside court.
Orr said he agreed to testify after seeing news reports about the prosecution, and he contacted the defence lawyer to offer his expertise.
"It seemed to me as a chemist that this was another chemist making a joke," he said outside of court regarding the alleged threat.
Earlier in the day, an officer who sought a Canada-wide warrant for Phillips said he feared the accused would harm officers if he was stopped during his trip to Ottawa.
Const. Marques Reeves of the Halifax Regional Police testified in Nova Scotia Supreme Court he was concerned for the safety of police officers who might come into contact with the accused as he travelled from his home in Halifax to the national capital in January.
Phillips was arrested in an Ottawa hotel on Jan. 21 after police found a large stockpile of his chemicals in two locations in Nova Scotia.