SAINT JOHN, N.B. -- Patterns of use on electronic devices in Richard Oland's office are being scrutinized by Crown prosecutors in an attempt to pinpoint what time the multi-millionaire was bludgeoned to death.

Oland's son, Dennis, is on trial in Saint John for the second-degree murder of his father on July 6, 2011, and key to his defence is the uncertainty surrounding the actual time of the killing.

Dennis is the last known person to have seen his father alive. He visited Richard at his uptown Saint John office late in the afternoon of July 6, staying an hour and leaving at about 6:30 p.m. He then headed home to the suburb of Rothesay on the outskirts of the port city.

A central question in the case: Was his father dead when he left? Or did he die later, in accordance with an earlier witness at the trial who said he heard loud thumps and crashes coming from Richard Oland's second floor office sometime between 7:30 and 8 p.m. that night?

The later time would exclude Dennis Oland, 50, as the killer. He was caught on security video shopping with his wife, Lisa, in Rothesay at that time.

Cell phone and computer experts on the stand at Oland's trial on Thursday said computers in Richard Oland's office fell idle shortly after Dennis arrived for his visit at around 5:30.

Payman Hakimian, who is with the RCMP's technological crimes unit in Fredericton, told the trial the last key stroke on Richard's personal computer was at 5:39 p.m. on July 6, 2011.

Under questioning by defence lawyer Alan Gold, Hakimian said his analysis cannot detect more subtle computer activity, such as using the up and down arrows on a keyboard to scroll through material.

Hakimian also told Gold that he downloaded hundreds of pages of data from Dennis Oland's home computers as well as those of Richard Oland. He said all of the data was sent to the Saint John police for examination. Nothing incriminating was found.

Not only was there no more computer activity in Oland's office after Dennis arrived for his visit, the prominent businessman and former executive at Moosehead Breweries Ltd. stopped sending and answering texts and calls on his cell phone -- the only item taken from the crime scene.

Sylvie Gill, an investigator with Rogers Communications in Montreal, went through call records at the trial, records which showed the date and time of all phone calls and text messages sent and received on Richard Oland's iPhone on July 6 and 7.

"The last communication was an incoming text message at 6:44 p.m.," Gill told the court, referring to a text sent by Diana Sedlacek, a real estate agent with whom Oland was having an affair.

The court already has learned this last message from Sedlacek, received by Oland's phone, read: "You there?" Gill said the site of the cell tower that message pinged off was "Rothesay Road, in Rothesay."

It would have been around the time Dennis Oland was in Rothesay, having left his father's office a few minutes earlier.

Richard Oland did not answer Sedlacek's message and after that last communication, the phone went dead. All incoming phone calls went directly to voicemail and text messages "were not delivered to the device," Gill said.

The phone has never been found.

Dennis Oland has pleaded not guilty to murder. His father, Richard, died from repeated sharp and blunt force blows, mostly to his head. The 69-year-old businessman was found lying dead on the floor of his office on July 7, 2011.

This is Dennis Oland's second trial. He was convicted in a jury trial in 2015 but that verdict was set aside on appeal and the new trial ordered.

The trial is expected to last until mid-March.