As brother AtlLaw suggested, it would be easy enough for the forensics lab to plot with a high degree of certainty. Whether they would make the effort or not considering how minor the outcome was remains to be seen.
No idea how far away the highway/other business you mentioned are, but IMO if it was a whimpy 380, it wouldn't carry much distance without lobbing it. It also wouldn't effect much damage from distance having lost much of its energy.
First, I want to express my concern for the person and his family that found a bullet in their home. That is a very scary thing and you have every right to be concerned and want to figure out who endangered your family.
Unless one really "knows" the cartridge, I think that an exact trajectory calculation would be very difficult, because you would literally need to calculate dozens of them.
The statement was that it looked like a "380." Unless the bullet was very light, like a 65 to 75 grain bullet, it could have been a variety of different cartridges.
The .380 Auto cartridges is really a 9mm bullet, with a diameter of .355 to .357 typically depending upon if it is jacketed or cast lead. The 9mm Luger or 9x19 is also a 9mm bullet. There are a bunch of other "9mm" cartridges, but none are very common. I can purchase commercial ammo 9mm Luger and .380 ammo with very similar bullet weights close to 95 to 100 grains. Since the bullet mushroomed and struck something, it may have lost some weight. There are probably dozens of 9mm bullets from different manufactures for a given bullet weight, finding the right one might or might not be tricky. The 9mm and .380 Auto will have different trajectories. There are also +P loads and hand loads all with different trajectories. Then there 38 Super (9mm) bullets and .357 Sig bullets, generally heavier, but sometimes can be hand loaded in light bullets and even faster velocities and flatter trajectories.
Now we move onto .38 Special, .38 Special +P, and .357 Magnum rounds that have bullets with diameters of about .357 to .359 inches. They all have different trajectories and diameters fairly close to each other and the 9mm bullet.
Now if the bullet can be clearly identified as say a Remington .380 Auto bullet, or as a 9mm magnum bullet of a certain manufacture, and one assumes that it is a commercially loaded ammo, then one could go to published data on the factory loaded ammo from an assumed barrel length or firearm and then calculate a trajectory. One would also need to recognize that there significant difference in the trajectory of a .380 Auto fired from my KelTec P3AT or from my Husquavarna Model 1907, which had a bushing installed when imported to convert if from 9mm Browning Long to 9mm Browning Kurtz (i.e. to .380 Auto). So even if you figure out the bullet assuming a factory load, the firearm might change the trajectory.
Now we can talk about air temperature, wind, and a host of other variables to change things even more.
The flip side of this is that the points you are interested in zeroing in on, say a close road and a far away daycare center, may or may not be distant enough that only one location might agree with most of the various "probably" trajectories.
You might go to your local library on see if they have a copy of Volume II of the Hornady Reloading manual, it has ballistic tables for just about every bullet and will allow you to try your hand at a few different hypothesizes. From doing several such calculations you may get a pretty good indication of the general area and you can turn that over to the police. They have a good website that can give you some of the basics you would want to consider.
http://www.hornady.com/ballistics/external.phpThe CSI TV shows are interesting, but I think the science they showcase is a little more complex than they make things out to be for the audience.
