Have you ever stopped and thought why cases get referred to the detective squad? One reason is that the perpetrator was nowhere to be found when the uniformed officers arrived. Other reasons range from unavailable or uncooperative complainants, complex issues such as embezzlements or other white-collar crimes, or other cases where criminality needs to be clarified. My question is this: is obvious "probable cause" a good reason for a detective to make an immediate arrest? I believe that the answer is a resounding "NO!"
Let's examine the first scenario. The uniformed officers arrive at the scene of a past robbery, and the complainant Ms. Ann Innocent tells them that her ex-fiancé Dom Perignon had robbed her at knifepoint not more that 5-minutes ago. Ms. Innocent provides the officers with a full pedigree, direction of flight, residence, and tells them that Dom works as a stockboy at ABC Liquors. The officers put Ms. Innocent in their car and canvass the area, visit the residence, and then ABC Liquors, but Dom is no where to be found. What would the officers have done if they had found Dom Perignon? Locked him up, right? Right. The mere fact that Ms. Innocent was providing them with the information that Dom had committed a crime gave the officers the probable cause to make the arrest.
Since no arrest was made, and Ms. Innocent wished to have Dom arrested and prosecuted for the robbery, the officers prepared their complaint report and left the case open for the detectives.
Young detective A.C. Ventura arrives for his 4x12, and finds the complaint report waiting for him. "A ground ball," he thinks. He looks at his squad commander, Lt. Columbo, and says, "Probable cause, and an easy collar, right?" Columbo provides him with a surprising answer; "Kid, you ain't in uniform no more. We should be looking past "probable cause" (see Bill of Rights, 4th Amendment) before we make an arrest."
Does this mean that detectives are required to prove cases beyond a reasonable doubt? No, that is left for trials. But in my opinion, detectives have the obligation to thoroughly investigate all of their cases. In the case of Ms. Innocent, Det. Venture should interview her; canvass for and interview any witnesses; search for and safeguard any evidence (security cameras from the local convenience stores, etc.); and attempt to locate and interview the suspect, keeping in mind that if Perignon is taken into custody or made to feel that he is not free to leave, he must be advised of Miranda (see Miranda v Arizona).
Investigations require a systematic approach to review all known facts, discover unknown facts, document them both, and if appropriate, make an arrest. This should hold true for every case that we become involved with, be it a homicide or a simple assault.
I can recall a simple assault case that occurred in New York in the mid-90s, involving two former professional basketball players. Back then, I had already retired from the NYPD, and I was well along with my civil private investigation career. In this case, "civil" meant that I did not (and still don't) handle criminal defense investigations. I made an exception for this one that I took on, as a favor to an attorney client who represented the pro basketball team in both this criminal and civil litigation.
Two very tall ballplayers from the Jersey side of the Hudson River were in a bar in the shadows of Madison Square Garden in Manhattan. Being conspicuously large, and often seen on TV, it was hard for them to remain anonymous for long. A few local fans began to chide them about the quality of their team and their personal abilities. No big thing for professional athletes. Happens all the time. It was about 2 A.M., and the ball players got up to leave. They began to cross 8th Avenue to get to their cars. A half-dozen 18 to 20 year old males who continued to harangue them followed them closely. I would guess that the weight distribution was about the same: two 7-foot tall athletes weighing a combined 600+ pounds, and six-half loaded half-pints who perhaps weighed in at 700. A couple of punches were thrown, a few pushes and shoves, and the six kids went home with a great story. The ballplayers went back through the Lincoln Tunnel, and gave serious thought to frequenting the bars in Secaucus in the future.