Staff Sgt. Nancy McLean of the Toronto police referenced the Trespass to Property Act and reasonable precaution to "ensure public safety" to justify the search of a G20 protester and the seizure of his goggles.

"We were there to provide a safe environment of the demonstrators," McLean said. "I did not need to be told what my authority was for that day."

McLean spoke Wednesday during day three of a $100,000 lawsuit against the Toronto Police Services Board for the alleged illegal search and detainment of a protester on the eve of Toronto's 2010 G20 summit.

McLean was the lead officer in the controversial exchange between police and protester Luke Stewart, who was trying to enter Allen Gardens for a peaceful protest on June 10, 2010. Stewart's bag was searched, along with the bags of anyone else trying to enter the park during that time.

"It was understood that if you wanted to come in to the park, we wanted to search your bags," McLean said. "Everyone let us except Mr. Stewart."

McLean explained the seizure of Stewart's goggles as part of an effort to seize any items that were "weapon-like" or that could be used to evade police tactics, such as tear gas.

"If [a situation has] resorted to tear gas, things have become volatile," McLean said. "I took it upon myself to decide for him that you don't want to be there when that happens."

Stewart, a 32-year-old university professor, launched the lawsuit over six years ago. He was the first witness of the trial, which started Monday, during which he described the exchange as "unfair and unjust."

The incident was recorded by a witness, which included direct exchanges between McLean and Stewart.

"I thought there was public interest in people seeing for themselves how the park and the demonstration was being policed," said Lisa Walter, the journalist who filmed the incident for Our Times magazine.

McLean said she acted as 'agent of the city'

McLean said her superior on duty told officers policing the G20 protests they had to be "vigilant in searches," which she and other officers in Allen Gardens understood needed to include bag searches.

"It was more like an understanding that we had — it was important to go to the park and screen people going into the park, she said.

McLean, who was a sergeant when the incident occurred in 2010, was the lead officer in the confrontation in Allen Gardens. She said police staff were trained with the "expectation of not only peaceful demonstrators but potentially some violent demonstrators as well."

She had tears in her eyes when looking at a photo of the turbulent summit.

"I'm sorry for the emotion, your honour," McLean said. "It's crazy daunting to look at that picture and think we could [manage] a crowd that size peacefully and that no one got hurt."

'I'm trying to understand the norm'

Stewart's lawyer, David Charney, cross-examined McLean for several hours Wednesday, asking numerous questions cornering whether she and the other officers in the park were given direction to conduct bag searches.

"What I'm struggling with is how it was that all officers in that perimeter came to that same understanding — was that because that's what they were told to do?" Charney asked the witness.

"Our concerns on that day ultimately was for the safety of demonstrators, the people attending, the safety of the officers. Based on the information we received, it was reasonable for us to request the search of bags," McLean said.

Charney also attempted to understand from the witness what officers' general training and requirements were for protests and demonstrations that had the potential to turn violent.

"I appreciate that you call this situation exceptional, but I'm trying to understand the norm," he said.

The hearing is scheduled for eight days, which will include testimonies from other Toronto police officers.