SAINT JOHN, N.B. -- The judge hearing the Dennis Oland murder trial in New Brunswick highlighted failings in the police investigation before sending jurors out Wednesday to begin deliberating a verdict.

Justice John Walsh also pointed out a lack of physical evidence tying Dennis Oland to the death of his father, well-known businessman Richard Oland. Walsh described the Crown's case - which took up the lion's share of 50 days of testimony from nearly 50 witnesses - as largely based on circumstantial evidence.

"This case in its totality is a circumstantial one," Walsh, of the Court of Queen's Bench, said during his final instructions.

Walsh said in order to find Dennis Oland guilty based on circumstantial evidence the jury must be satisfied beyond a reasonable doubt that it is the only rational conclusion that can be drawn from the evidence.

Oland has pleaded not guilty to second-degree murder.

The elder Oland, 69, was found dead in his Saint John office on July 7, 2011. He had suffered 45 blunt and sharp force blows to his head, neck and hands.

Dennis Oland, 47, looked grave and serious Wednesday as the four women and eight men of the jury left the courtroom.

"Thank you. We will await the jury's decision," said Walsh.

Walsh spent most of the last two days delivering his final instructions to the jury, going over testimony from trial witnesses and repeatedly warning jurors that they must be convinced of guilt beyond a reasonable doubt in order to convict.

"If you believe Dennis Oland's statement and testimony that he did not commit this offence, you must find him not guilty," said Walsh.

Walsh said even if the jurors don't believe Dennis Oland's testimony but are left with reasonable doubt, they must find him not guilty.

Walsh reviewed Dennis Oland's statement to police on July 7, 2011, as well as his testimony during the trial, then told the jury to assess the credibility of his evidence the same way as any other witness.

"I am only trying to assist you, not tell you what to decide," Walsh said.

Earlier Wednesday, Walsh told the jury to consider the adequacy of the police investigation.

He said the trial heard that police failed to prevent too many people from entering the crime scene, failed to protect against the use of the second-floor washroom before it could be forensically tested, failed to ensure the back door remained untouched before it could be examined, and did not ask a pathologist to determine if a drywall hammer was the probable murder weapon.

On Monday during his final summation, Crown prosecutor P.J. Veniot said that despite some shortcomings, the investigation by the Saint John police was sound.

The judge noted there was no physical evidence at the crime scene to connect it with Dennis Oland or anyone else. As well, there was no physical evidence linked to the crime in Dennis Oland's car, on his BlackBerry or on shoes seized from his home.

He said it's up to the jury to use common sense to assess what was found on the brown sports jacket Dennis Oland was wearing when the financial adviser visited his multimillionaire father on July 6, 2011.

Investigators found three tiny areas on the jacket that tested positive for blood. DNA extracted from those areas matched the profile of Richard Oland. One expert said the chance that the DNA could have been from someone other than Richard Oland was one in 20 quintillion.

However, the experts could not say how long the blood had been on the jacket or how it got there.

Walsh spent quite a bit of time dealing with the Crown and defence arguments on the time when Richard Oland was killed.

The Crown contends Richard Oland was killed between 5:45 p.m. and 6:30 p.m. when Dennis Oland was there, while the defence argues it was later in the evening when security camera video shows Dennis Oland and his wife shopping in nearby Rothesay.

Walsh said it was up to the Crown to prove that Dennis Oland was at his father's office at the time of death, and not up to the defence to prove he was elsewhere.

Walsh said the jury can return only a guilty or not guilty verdict on the charge of second-degree murder. He said the verdict must be unanimous and told jurors to "make every reasonable effort" to reach a verdict.

"Keep an open mind but not an empty head. Listen to what your fellow jurors have to say. Jurors are judges," Walsh said.

Walsh said it is up to the jury how late to deliberate into the evening.

The sequestered jury began its deliberations mid-afternoon. They met until after 8 p.m., when they decided to retire for the night. Deliberations were to resume Wednesday at 9 a.m.

Sheriff deputies have been assigned to ensure jurors have no contact with anyone outside the jury room until deliberations are complete.