Skip to main content
U.S. flag

An official website of the United States government

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.


Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Probable Cause (II) (MP3)


  1. Home
Audio File


Miller: Hey this is Tim Miller and Jennifer Solari. We’re back. We’re talking about probable cause. Jenna, how do agents establish probable cause? Do courts help us out in any way?

Solari: Well the courts have given us some guidelines to tell us what would be enough to establish probable cause to search based on various sources. We started off with a case called Aguilar, which was supplemented by a case called Spinelli so we use to call it the Aguilar/Spinelli test, which was really a litmus test until 1983. The courts required both a creditable source and a reliable basis of knowledge. By basis of knowledge, I mean how does the person know - the who, what, where and how of the criminal offense.

Miller: Who’s a credible source?

Solari: Law enforcement officers are presumed to be credible; so are victims and witnesses who come forward and identify themselves. Partners in crime are reliable. So are confidential informants, as long as they have a good track record.

Miller: Who’s a partner in crime - he doesn’t sound very credible?

Solari: No, it wouldn’t at first, would it. Let’s say I’ve been apprehended by police for a suspected offense - drug possession. I decided to tell them that John Doe is a drug distributor and they ask me how I know that. I say because I’ve been buying marijuana from John Doe every three days for the past four weeks. I explain that I go to his house and I buy it and I see the drugs on his kitchen table all the time. I know how he packages the drug.

I think the courts really have decided that partners in crime can be deemed reliable because if somebody’s going to incriminate himself, then there’s really no reason to do that just to make up information. It’s not in anybody’s best interest to incriminate them self just to get somebody else in trouble.

Miller: People aren’t likely to incriminate themselves unless it’s true.

Solari: Right.

Miller: What’s a basis of knowledge? Let me ask you that.

Solari: Again, it’s really just that - who, what, when, where and how of the criminal offense. The court wants to know how the source got the information and whether he got it in a reliable way. That’s not to say it has to be first hand information. That’s preferable; specifically, that this person has seen or heard or smelled the evidence, first hand. But, we can also rely on hearsay. What the court wants to know at the end of the day is this – was the information acquired in a reliable way.

Miller: Well, suppose a government agent gets a tip from someone who refuses to identify himself. Credible source?

Solari: No. Not an anonymous, tip alone. There’s got to be something more than that in order for it to be deemed reliable.

Miller: So, let me think about this for a minute. If a government agent gets a tip from an anonymous source that I’m selling narcotics out of my house, I don’t need to worry; right?

Solari: Not necessarily. And actually that’s why I say that Aguilar/Spinelli test was only a litmus test until 1983. Then we came upon the Gates case. That was a case in which police received a tip from an anonymous source in the form of a letter. The letter described very particularly how a couple in town was going about transporting drugs to and from a specific place. The letter was specific; it detailed how these persons, how these people would transport the drugs back and forth and actually predicted future events.

So the courts took a look at the Aguilar/Spinelli test and thought, this wouldn’t be probable cause because we can’t determine whether the source is credible, we don’t know who this source is, and we don’t know the basis of knowledge here again. But the letter seemed reliable, because it predicted future events that actually came true. The police went to great lengths to actually corroborate the information in the letter and to such an extent that the Court could tell the information was reliable. So the courts overruled the Aguilar/Spinelli test, in so far as it was the only test, and said that now were going to consider the totality of the circumstances.

So when we do get an anonymous tip - standing alone that’s not enough. But, if the police through independent investigation can corroborate some or all of that information, then it’s probably going to be enough to be deemed reliable.

Miller: Okay. Now, you said that the courts prefer search warrants, right?

Solari: Absolutely.

Miller: And, government agents gather the facts to establish probable cause to support the warrant, correct?

Solari: Yes.

Miller: How do the government agents get that information before the judge to get a search warrant?

Solari: To request a search warrant, the agent’s going to fill out a Search Warrant Application. Part of the application they’re going to have to write and swear to is an affidavit that sets forth all of the facts and circumstances that establishes probable cause.

Miller: Can you tell me a little about the affidavit and what it might contain?

Solari: Sure. The affidavits introductory paragraph introduces the agent who’s requesting the warrant. It goes on to explain who the agent is; where she went to school; how long she’s been in law enforcement; what kind of training and experience she’s had.

It will probably be of interest to the judge to know what kind of experience the officer has had in law enforcement, how she knows certain things about this case, and why she should be deemed credible. Second, the agent’s should establish that a crime has been committed or is going to occur. The agent should set forth for the court that there is some evidence of crime to be found somewhere. And then, they’re going to have to establish a nexus between the evidence of crime and the place they want to search.

Miller: Let’s assume that you’re a Federal Magistrate and that I’m a government agent and that I want to get a search warrant to search a house. What information would you expect to read in my affidavit?

Solari: Alright, first I’d expect you to tell me a little bit about yourself, so that I can figure out who you are and establish your credibility.

Miller: Okay well lets pretend that I’m Tim Miller, well I am Tim Miller, but …

Solari: (Laughing)

Miller: Let’s also pretend that I’m a Naval Criminal Investigative Service Agent; that I’ve been an agent for about 10 years; that I have authority to investigate criminal crimes; that I’ve investigated about 200 felonies; and, that I’ve executed about 50 search warrants.

Solari: Alright well then I’d expect you to tell me where it is that you’d like to search.

Miller: Let’s say it’s a house located at 123 Main Street in Brunswick, Georgia.

Solari: Alright, what are you looking for?

Miller: Ah, marijuana.

Solari: Okay well marijuana is contraband, so that certainly is something you’d be authorized to seize. How do you know that marijuana is located at 123 Main Street, right now?

Miller: Let’s say that an informant told me.

Solari: Well I’m going to need something more than that. I’m going to need you to establish the credibility of the informant.

Miller: Okay, well we’re getting back to those facts that establish the probable cause, is that correct?

Solari: Right.

Miller: Do I have to tell you my informant’s name?

Solari: You don’t have to tell me his name, but if you don’t, I need you to establish that he’s got some sort of reliable track record as far as providing you good information in the past.

Miller: Let’s call him Mr. X. Let’s say that I’ve known him for two years, he’s worked for me as an informant on four other narcotic investigations, he’s never lied to me before, and the information that he’s provided to me in the past has led to two arrest for illegal possession of marijuana.

Solari: Okay, well he sounds like a credible source then. How does your informant know this? What’s his basis of knowledge that there’s marijuana in the house?

Miller: Let’s say that Mr. X told me that he went inside at 123 Main Street yesterday. That he saw a green leafy substance in a plastic bag. Let’s also say that he’s seen marijuana before on multiple occasions. Uh, the occupant of the premises also asked Mr. X if he wanted to buy the bag and referred to it as “herb.” From my training and experience I know that “herb” is a common street name for marijuana.

Solari: Okay, well that sounds good to me. I know who you are, that you are a credible agent, and you’ve established for me that your source is credible. You particularly described for me where you’d like to search, and the things that you’d like to search for. I think you set forth facts to establishing that evidence of a crime, specifically marijuana, will be located in the place to be searched, 123 Main Street. So I’d give you that warrant.

Miller: Okay, let’s take a break and we’ll come back and we’ll talk a little bit more about search warrants in itself.

Solari: Okay.