SAINT JOHN, N.B. -- An expert on cellphone towers says the chances are "very small" that Richard Oland's cell phone was still in his Saint John office when it received a final text message on the day the multimillionaire was killed.

Joseph Sadoun, a consulting engineer for cellular companies, told Dennis Oland's trial on Tuesday the general rule is that cell phones communicate with towers that have the strongest signals, and those typically are the closest.

On July 6, 2011, the day Richard Oland was bludgeoned to death in his uptown Saint John office, the final message to his phone at 6:44 p.m. pinged off a tower in Rothesay, a bedroom community on the outskirts of Saint John where Richard Oland's only son, Dennis, lives.

Dennis Oland, 50, told police he left his dad's uptown office at around 6:30 p.m. on July 6 and headed home. He is the last known person to have seen his father alive.

If the cell phone evidence is accurate, it suggests Richard Oland's iPhone may have left the office and was in Rothesay at about the same time as Dennis Oland. Prosecutors are suggesting that Oland, for some reason, took his father's phone from the crime scene.

The cell phone was the only item taken from the office where Richard Oland was killed despite a number of valuable items at the scene. It has never been found.

Sadoun was asked by Crown prosecutor Derek Weaver how likely it was that the phone was still in Richard Oland's office in the city when the final text message came in.

"The likelihood is very small," Sadoun said.

He said terrain and obstacles such as buildings between the urban tower and the suburban tower make it unlikely the message would have bounced off Rothesay into the Oland office.

But a "very small" chance provided a sizable opportunity for defence lawyer Michael Lacy to make the point that it is still possible for towers other than those closest to a cell phone to service calls and texts.

"Reality is often the exception to the generality," Lacy said in his cross-examination of Sadoun, who agreed probability maps do not always reflect the real world.

Sadoun reviewed test call data gathered by the Saint John police as they tried to establish patterns of use for cell phone towers.

He found most of the test calls behaved as expected, using the closest towers with which to communicate. But several calls did not behave as expected and pinged off more distant towers, including several calls from the Rothesay area.

"Estimates of likelihood can be wrong," Lacy said.

Sadoun said it is "not a yes or no" answer as to whether a call to Oland's cell in his office could have pinged off the Rothesay tower instead of the nearby Saint John city tower, but he insisted it is "unlikely the case."

The final text received by Richard Oland's phone was from Diana Sedlacek, the woman with whom he was having an affair. "You there?" it said. The text was never answered and following that the iPhone essentially went dead.

It is key evidence for prosecutors who are using cell phone records to try to establish that Richard Oland was dead when his son left the office that day at about 6:30 p.m.

Dennis Oland, an investment adviser, has been charged with the second-degree murder of his father. He was convicted of the crime by a jury in 2015 but that verdict was set aside on appeal and the new trial - this time before judge alone - was ordered.

Sadoun showed the trial a series of slides that outlined coverage patterns in Saint John and the Rothesay area.

Just down the street from the office where Richard Oland was killed is a large building with cell towers on its roof. If the cell phone was still in the office when the last message came in, Sadoun's maps indicate it most likely would have pinged off the urban tower, not Rothesay.

The trial is expected to last until mid-March.