They call them split-second decisions for a reason.
Whenever a serious crime is reported and no one is arrested straight away, the same question follows. The police were right there. They spoke to people. So why did nobody get arrested?
The answer is a legal standard called reasonable grounds, and it is the most misunderstood threshold in Canadian policing. I had to meet it myself before I could put my hand on anyone, and I spent twenty years teaching it to college law enforcement students.
Here is what it actually requires, why it cannot be lowered, and why the officer standing in that alley has about one second to get it right.
Day one, 1975
I was sworn in on 27 October 1975. I was eighteen years old. Three days earlier I had been sitting in a high school classroom.
As soon as the swearing-in was done they handed me two things: a New Testament and a Criminal Code. The personnel sergeant told me to memorise section 450 of the Criminal Code, and three things inside it.
1. A peace officer's powers of arrest without warrant.
2. The definition of reasonable and probable grounds, which everyone called RPG then.
3. The definition of mere suspicion
Then he handed me the Police Act of Ontario and told me to memorise the offence of neglect of duty, and to pay attention to the consequences. One of them is getting fired.
He said nothing was more important than memorising all of it.
A few weeks later I was at the Ontario Police College for fifteen weeks of basic recruit training. On day one the instructor told the class to memorise exactly the same three things, and said plainly why: it would keep us from being sued for false arrest.
That is how seriously this standard is treated. Before the uniform fits properly, before you have taken a single call, you are expected to know the line between what lets you ask a question and what lets you take away a person's liberty.
What changed since then, and what did not
Over my fifteen years in policing and the thirty-six since, the words moved around. The substance did not.
• Section 450 became section 495. Same powers of arrest without warrant, new number.
• Reasonable and probable grounds became reasonable grounds. They cut out “and probable”. I looked it up to be sure, and the case law confirms the definition itself never changed. They shortened the phrase, not the standard.
• Mere suspicion kept its definition entirely. It has never changed.
• The Police Act became the Police Services Act, and then the Community Safety and Policing Act. Neglect of duty is still in there, and it still carries severe consequences.
I have carried all of it since 1975 and never forgot it, and I have kept teaching and writing about it since I left policing in 1990.
What reasonable grounds actually require
Reasonable grounds to believe is what the law demands before an officer can arrest someone without a warrant, and before a justice will sign a search warrant.
It requires an objective totality of circumstances showing a reasonable probability that an offence was committed and that this particular person committed it.
The word doing the work in that sentence is objective. The test is not what the officer believes, or how strongly he feels it standing there at two in the morning. It is what a reasonable person, looking at the same facts, would conclude.
That is why grounds have to be built out of things that can be written down and defended months later under cross-examination. Identification. Forensic results. Witness statements. Recovered physical evidence. A feeling in your gut is not a ground. It never was.
What mere suspicion is
Mere suspicion is the state below the line. Something about the situation bothers you, but the facts do not add up to probability.
Mere suspicion does not authorise an arrest. It never has.
Both reasonable grounds and mere suspicion are abstract concepts. That is the difficulty. They are definitions, and you are applying them on a street at two in the morning with incomplete information and no time.
Three levels, not two
The law now recognises a middle step between the two I memorised in 1975.
• Mere suspicion. A feeling without articulable facts behind it. Authorises nothing.
• Reasonable suspicion. Articulable facts suggesting the possibility of criminal activity. Supports a brief investigative detention and questions. Not an arrest.
• Reasonable grounds to believe. An objective totality of circumstances showing a probability that a specific person committed a specific offence. Supports an arrest, and a search warrant application.
The difference between the second and the third is the difference between possibility and probability. An officer who has reached the second but not the third may stop and ask. He may not arrest. That single line decides a great many cases.
A case study I taught for twenty years
Every case study I set for my college law enforcement students started with the same sentence. You are a street cop in this case study.
You are working the midnight shift, midnight to eight, assigned to patrol the downtown district of your city.
At two in the morning a pedestrian on the sidewalk sees you, stops, looks directly at you, then turns and sprints down an alley in the opposite direction.
You chase him on foot. This, incidentally, is why you get yourself into the gym and into the best shape of your life.
After a short sprint he stops. You stop. You are now face to face in an alley.
Five questions. They were on the arrest exam.
1. At this point, do you have reasonable grounds to arrest him without a warrant under section 495?
2. Do you have mere suspicion?
3. Do you have grounds to search him for a weapon to protect yourself?
4. What if you let him go and he kills someone an hour later. Have you committed neglect of duty?
5. What if you never chased him at all and just kept driving. Have you committed neglect of duty?
Sit with those for a moment before reading on.
Why the alley is harder than it looks
Most people answer the first question instantly, and most people answer it wrong in both directions.
Flight is a fact. It goes into the totality. But flight on its own does not establish a probability that this man committed a particular offence, because there are lawful reasons a person runs from police, and a court will say so. At the same time, flight is not nothing, and an officer who treats it as nothing is making a different mistake.
The third question is a separate test entirely, and that is the point of asking it. Officer safety is not the same question as arrest, it has its own threshold, and an officer who collapses the two will lose both the search and the case that followed it.
Questions four and five are the ones students never expect, and they are where most of the real risk lives.
The half of the job nobody talks about
Every public conversation about arrest powers is about police doing too much. Almost nobody discusses the other side of it.
Neglect of duty is a disciplinary offence. It survived every rewrite of the legislation, from the Police Act to the Police Services Act to the Community Safety and Policing Act, and it still carries severe consequences, including dismissal.
So the officer in that alley is standing between two failures. Arrest without reasonable grounds and the arrest is unlawful, the evidence is at risk, and the case may be destroyed. Walk away from something he should have acted on and he may have neglected his duty, with a consequence of its own.
Neither mistake has a safe side. That is the job.
What happens if you get it wrong
Section 8 of the Canadian Charter of Rights and Freedoms protects against unreasonable search and seizure. Section 9 protects against arbitrary detention. An arrest made without reasonable grounds can be an arbitrary detention.
Under section 24(2), evidence obtained as a result of that breach may be excluded at trial.
So an arrest made too early does not merely risk a complaint. It can destroy the prosecution of the very offence the officer was trying to solve. The statement becomes inadmissible. The search becomes inadmissible. The case collapses, and it does not come back.
That is what the personnel sergeant meant in 1975, and what the instructor at the Police College meant, and neither of them used the word Charter, because it did not exist yet.
How reasonable grounds are actually formed
Done properly, this is a process, not a feeling.
You take what you observed, what you were told, and what you recovered, and you test whether those things together reach probability rather than possibility. Then you record the reasoning in a form that will still stand up months later when a defence lawyer goes through it line by line.
That process is what my textbook sets out: the statutory and Charter boundaries an officer works inside, how a scene and its evidence are preserved so they stay usable, how interviews are conducted so statements survive, the matrix for turning raw observation into articulable grounds, and how all of it is written into a warrant application and defended on the stand.
The five questions in that alley are reasonable grounds 101. They are not the whole story.
Who has to get this right
Police Foundations students, who are examined on it. Patrol officers and cadets, who apply it in seconds on the street. Detectives, who have to structure it into search warrant applications. And paralegals and defence investigators, who read police disclosure looking for the precise point where the grounds do not hold.
Don't blink
Section 495 of the Criminal Code, the formulation of reasonable grounds, and the identification of mere suspicion are complicated street decisions that have to be made in the blink of an eye.
Public frustration when no arrest follows a serious crime is not unreasonable. Families are hurt, people are frightened, and a standard explained in legal language can sound like an excuse.
But the standard is not a formality and it is not a loophole. The answer to a hard decision made badly is not a lower standard. It is better training in how to reach the standard quickly, and how to document it properly when you do.
Don't blink.
Frequently asked questions
What are reasonable grounds in Canadian law?
Reasonable grounds to believe is the standard Canadian police must meet before arresting someone without a warrant under section 495 of the Criminal Code, or applying for a search warrant. It requires an objective totality of circumstances showing a reasonable probability that an offence was committed and that a specific person committed it.
What is the difference between mere suspicion and reasonable grounds?
Mere suspicion is a feeling without articulable facts behind it, and it authorises nothing. Reasonable grounds to believe requires an objective probability that a specific person committed a specific offence, and is what the law requires before an arrest.
What is reasonable suspicion, and how is it different?
Reasonable suspicion sits between the two. It rests on articulable facts suggesting the possibility of criminal activity, and supports a brief investigative detention and questions. It does not support an arrest.
Can police arrest someone just for running away?
No. Flight is a fact that goes into the totality of circumstances, but on its own it does not establish a probability that a particular person committed a particular offence. There are lawful reasons a person runs from police.
What happens to evidence if police arrest without reasonable grounds?
Evidence obtained as a result may be excluded at trial under section 24(2) of the Charter. Statements, search results and seized items can all become inadmissible, which is why forming grounds correctly protects the prosecution as much as the accused.
What is neglect of duty?
It is a disciplinary offence for police in Ontario, now found in the Community Safety and Policing Act, previously in the Police Services Act and the Police Act. It carries severe consequences including dismissal, and it is the risk that runs in the opposite direction to an unlawful arrest.
Which section of the Criminal Code covers arrest without warrant?
Section 495. It was numbered section 450 until the Criminal Code was renumbered, and the powers themselves did not change.
This article is general legal education about how a standard in Canadian criminal procedure works. It is not legal advice, it is not a comment on any active investigation, and it makes no claim about the guilt or innocence of any person.
Gino Arcaro was sworn in as a police officer in October 1975 at the age of eighteen, served fifteen years including as a detective, and taught college law enforcement students for twenty years between 1990 and 2010. He is the author of Criminal Investigation: Forming Reasonable Grounds
