Defence lawyers for accused letter bomber Guido Amsel cross-examined a Winnipeg Police Service identification officer at length Thursday in an effort to weaken the integrity of evidence seized from three crime scenes. 

Central to much of the testimony was a plastic pouch that allegedly housed an explosive device which detonated at the Petersen King law office on River Avenue, July 3, 2015, seriously injuring lawyer Maria Mitousis.

The pouch has been described as one of the most important exhibits in the trial. Once seized by police, the pouch and other exhibits were all sealed in zippered plastic bags to avoid contaminating any evidence.

Const. Brian Neumann testified he opened the evidence bag containing the pouch prior to the start of the trial to ensure it contained what he thought it did. Neumann said his confusion arose from an RCMP identification number different from the one he had assigned to the exhibit.

But defence lawyer Saheel Zamen seized on Neumann's action as a sign that he was not confident evidence handling protocols had been maintained.

"If you were so convinced in the handling of exhibits and the securement of exhibits as well, there would be no need for you to check into the bag to make sure it was there," Zamen said.

"I think if I'm coming to court with probably my most important exhibit for court, I would want to ensure that I am bringing that exhibit to court," Neumann countered. "Call me hyper-vigilant when it comes to ensuring that the exhibit is in there."

Amsel, 51, has pleaded not guilty to five counts of attempted murder and several explosives offences in connection with bombs that were delivered to two law firms on River Avenue and Stradbrook Avenue, and to his ex-wife's workplace on Washington Avenue in July 2015. The bombs sent to Stradbrook Avenue and Washington Avenue were safely detonated by police.

Neumann told court he attended to Petersen King at 11:45 a.m., more than an hour after the bomb blast, and was tasked with crowd surveillance. He didn't enter the law office to document the scene and seize exhibits until 4:20 p.m.

Zamen alleged Neumann had no idea how many bomb unit officers had entered the building before he did, possibly contaminating the scene. 

"So a lot of people could have potentially walked through from the bomb unit," Zamen said.

Neumann said it was up to the bomb unit to decide when it was safe for other officers to enter the building.

"We aren't going to charge blindly into a scene," Neumann said. "Safety is paramount."