Tuesday marked a tense start of the second week of the Andrew Berry murder trial.

There were heated exchanges between Berry's lawyer Kevin McCullough and Const. Piotr Ulanowski, the first officer on the scene, Christmas Day 2017.

Berry is accused of murdering his daughters Chloe, 6, and Aubrey, 4. The girls were found dead in his Oak Bay apartment. Berry has pleaded not guilty to second-degree murder charges.

On Tuesday, McCullough was critical of the police investigation and alleged that Ulanowski's work was incompetent that night. It's an allegation the officer denied.

McCullough challenged Ulanowski about leaving the door to Berry's apartment unsecured and unattended for five minutes, even when he thought it was a crime scene. 

The lawyer called it a mistake that could have let the killer get away. While Ulanowski acknowledged it was a mistake, he denied it was incompetence.

Later, in a heated exchange, McCullough suggested the officer was uncomfortable on the stand because he didn’t record opening Berry's apartment door in his early notes from the night.

"This is uncomfortable because I have to reference dead kids that remind me of my own," Ulanowski replied. "The only thing I wanted to do that night was go home to my kids."

"You realize he's on trial for murder, don't you?" McCullough said, with a raised voice.

"You have attempted to cover up your incompetence with the idea that what you saw freaked you out," he said.

McCullough also questioned the officer about the crime scene, and Ulanowski acknowledged he likely tracked blood from the apartment bathroom, where Berry was found in the bathtub, out into the apartment's hallway on his shoes.

Berry's lawyer was also critical that the officer's recollections could be contaminated by talking that night with other officers who'd been on scene, before giving a statement about the night's events.

Ulanowski responded, "I'm not sure why you're berating me with this. I had a mental health [session] before I got home."

McCullough later accused Ulanowski of "shading" his evidence "to try to convict Mr. Berry." The officer rejected the allegation.

The trial is scheduled to last four months. Ulanowski is expected to be on the stand Wednesday for more cross-examination.