I recently met with a young man of 19 that was trying his best to write a mystery story for school, that took place in the early 1970s. There was a lot of police interaction throughout his writing. His main trouble was he was only familar with the police of today and missed several points.
So I thought I would spell out a few items here for you younger writers, that may not have been born in the 1960s or 70s. Some departments were of course further advanced and equiped than others, but most were still pretty low tech.
Then: The average LEO in those days carried a .38 cal. revolver, either a Smith and Wesson or a colt, (5 or 6 shots respectively) usually a 4 inch barrel and it was gun metal blue with wooden grips.
Now: Most officers now carry either a 9 mm or .40 cal. semi automatic. Some department autothorize the use of either a .41 or .45 cal. weapon. Most weapons hold from 10 to 15 rounds and most often two additional clips are carried. Color of most weapons are black and are made either of steel or a composite material.
Then: Most every officer had some type of car for a cruiser.
Now: The patrol vehicles can be a car, truck, 4 x 4 vehicle or even and ATV.
Then: Most every department had the wailing siren.
Now: Most departments use a variable siren that has a warble, high/low and/or amplified horn.
Then: Most parts of the country used the 10 code/signal system. Like 10-4
Now: You will have to check and see what your chosen area is using. Most of the country is going to a new standardized code system.
Then: There was no CSI. They could match foot prints, finger prints and blood types. There were a few other things that were used like castings.
Now: The sky is the limit. With all of the automated computerized data bases and computers in the vehicles. Many things are almost instataneous. DNA wasn't used in criminal cases until 1988 in England.
Then: Most areas had radios in the crusiers. Once you were away from the car you were on your own. Many departments used walkie talkies to communicate from the field back to the cars. They were usually pretty large and bulky.
Now: Quite dynamic systems in the cars and small personal clip-on mics that communicates through the car system to the base or to other units. Pluse the use of cell phones.
Then: There were Polaroid cameras for immediate development in the field. Often of poor quality. SLR 35 mm film camers and 4 X 5 graphic film cameras. The last two required for the film to be developed and processed. Everything was shot in Black & White. The courts felt color was to gory.
Now: Everything instant with digital cameras of all quality including cell phones. WIth cell phone photos the picture can be shot and immediately emailed to another location.
This is just a few of the things I can think of that may make a difference in your story telling. As I think of more I will either add them here or make another post. Any questions about othe items send me a PM and ask away. I will do my best to help you out.