Question? Who told you that assaults by strangers were rare?
From what I can recall from college, assaults by strangers are almost as common as assaults by someone known to you. Of course, a lot will depend on the type of assault that we are talking about. Domestic abuse is almost entirely committed by someone you know. However, if you are involved in an armed robbery, in another locality from your home, it is unlikely that you will know the perpetrator. Sexual assault can fall either way. You may have met the rapist before, but then again, a lot of women are stalked and attacked by someone who only knows them and they could not identify them prior to the attack. If we take a standard drive by, some of the victims may know the perpetrators while others, innocent bystanders, may have no idea who shot them.
Simply put, they can track your cell phone if it is in use. This technology has been around long before cell phones came into being. Basically, cell phones are the equivalent of radios, which can be tracked or located with the proper technology. Newer cell phones have GPS, Global Positioning Systems, in them. What these systems do is to locate a series of satellites, in orbit around the Earth, and use a form of triangulation to determine your location. This has been in use since at least the 1980s. Back then, though, these units were bigger than most cell phones are today. In any event, the majority of them require activation in order to locate your position. If they are off, then they cannot transmit and receive data. For the most part, active use of the GPS drains your battery so it tends to be optional.
At this point, I am stretching beyond my knowledge due to the progress of technology. There would be two ways that your phone could be tracked. The first, and probably most common, would be to use the signal towers that you connect to to give a location. This would be an estimate, but considerably cheaper. The second would require major government technology that could track the information in your cell phone, on or off. To the best of my knowledge, this is not available to law enforcement or the general public. The best you can get is a tracker that will connect to the satellites periodically and then record the information for later retrieval. This means that they would have to retrieve the tracker and download the information into a computer before they would know where you were. I do not know of any real-time trackers that are not in use by the government for special operations.
Tapping, however, is a piece of cake. There are laws against it, but then it is still done. The BS about requiring a warrant to tap your phone is a crock of legal whooey. Yes, there are laws in effect, but my experience with law enforcement has been that they disregard these laws, or obey them, when it fits their needs. The federal government has made it illegal for scanners to be able to tap cell phones, unless illegally modified, but they can be used to eavesdrop on cell phones and wireless phones, without modification, if you have the right know-how. The police, however, do not need to worry about such inconveniences because they are the law. In most cases, all they have to do is flash the badge and they can get whatever they want. Very few people have the money to fight this in court, especially when the courts are also part of the state, like the police. Since 9/11, they can justify nearly anything with the right wording.
If they do not believe your side of the story, about the assault, then they won't waste their time. For that matter, even if they do believe your side of the story they are unlikely to worry with it unless you have powerful connections or good deal of money. The exception to this is if you are dealing drugs, which is all the government cares about today, in which they will do nearly anything to get a conviction. If this was a case of rape, it is unlikely to go anywhere anyway. From the police all the way to the courts, they simply don't care about women. Sad but true, and the fact.
Police patrols tend to be predictable. They will be out heavy on Friday and Saturday because those are prime drinking nights. Sundays onward tend to be less watched. Precipitation tends to put them in central locations so they can work at a lot of traffic reports. Today, it's rare that they actually patrol. But, for you to actually be followed, and to see them, that would only be in the event that you are the president's daughter, and then it would be Secret Service agents. They simply do not have the manpower to do such things. I suspect, but from my experience, that your boyfriend had something to hide and was worried that they might catch him.
Hope this helps some,