One of the first police officers to attend the scene of the Douglas Garland triple murder trial continued his testimony on Thursday for day four in Calgary.

56-year-old Douglas Garland is charged with three counts of first-degree murder in connection with the deaths of Alvin and Kathy Liknes and their grandson Nathan O’Brien.

On Thursday, the court heard again from Cst. Derek Alexon, who continued his testimony about what he saw at the crime scene at the Liknes home. He said that he didn't speak to any other officers who went into the home before him or Jennifier O'Brien, Nathan's mother.

Alexon answered questions from the defence about the possibility of contaminated evidence and admitted that there would be a chance of that given that O'Brien and first responders would not have had the benefit of the protective gear that forensic teams do.

According to the Crown, Garland had 'started to research a specific lock, the Schlage BE365' 17 days prior to the murders.

Monte Salway, an expert locksmith who lives in Indiana, testified on Thursday regarding how difficult it would be to bypass the Schlage BE365 lock that had been installed on the side door of the Liknes home. According to Salway, the lock could by opened in less than five minutes depending on the expertise of the person attempting to bypass the lock.

Salway was asked to examine the lock on the Liknes home and determined the cylinder had been altered. "That has obviously been turned," said Salway. "Additionally, two holes noted." The lock expert said the holes would not have been drilled by an experienced locksmith as the chosen location would likely damage a number of internal parts.

Cst. Craig Adolph of the forensic crime unit and Cst. Brian Clark of the cyber investigation team were also called on Thursday. Adolph had examined the locks on the exterior doors of the Liknes home and Clark collected digital evidence from the home's internet router.

The Crown said at the beginning of the trial on Monday that the Liknes’ and their grandson Nathan O’Brien were violently take from their beds and killed them on the farm owned by his parents near Airdrie.

Their bodies were burned in a barrel and disposed of, the prosecution says.

The trial is scheduled to last five weeks.