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This is the question that I got for my assignment:

In a square room with 7 m-long sides, five people (black circles) have shot at random people. They all had two bullets and killed two people (red) in the crowd. Other people were not hurt (green). CCTV recordings show the positions of the shooters, of the victims and of the bystanders just before the tragedy. The family of the victims now want to find out who killed whom. You’re in charge of the investigation: can you provide an answer? Is there a unique solution?

We assume that all individuals can be represented as circles of radius r = 30 cm.

Data set giving the exact positions of the criminals, of the victims and the bystanders will be provided.

These are the coordinates of the bystanders, while the killer and the victim coordinates is ignored for a while,

bystander= {{6.3796, 3.74287}, {2.34476, 0.782156}, {5.31902, 1.07837}, {4.89694,  3.21151},
            {2.34862, 6.6094}, {5.6307, 4.63465}, {5.17291,6.01456}, {3.54308, 0.672974}, 
            {0.800921, 4.96581}, {2.52666,2.49223}, {3.21395, 5.70293}, {1.30108, 0.35637},
            {1.58679,5.55946}, {4.37022, 2.80391}, {3.34787, 4.5426}, 
            {4.35362,1.40922}, {0.488143, 5.7477}, {3.16706, 6.56368}, 
            {6.53454,5.2199}, {6.51183, 6.30547}, {2.19508, 1.58369}, 
            {4.01932,5.86994}, {0.349634, 0.328767}, {2.45308, 3.59521},
            {4.17676,3.96843}, {3.7773, 3.05002}, {0.48129, 2.81047}, 
            {3.09964, 3.27978}, {2.63825, 4.18187}, {2.71531, 4.86246}};

And I tried to do the ListPlot command,

plot1 = ListPlot[bystander, Frame -> True, AspectRatio -> 1,
        PlotMarkers -> {Graphics[{Opacity[0.1], Green, Disk[]}], .3},
        PlotRange -> {{0, 7}, {0, 7}}]

The solution that I got in my mind is that I need to show the possible victims that had been killed by the killer, but the bullet does not travel through the overlay of the bystanders.

So, I decided to use Union on the bystander locations, but I don't have any idea on how to make a union of a huge number of green circles. Is there any other commands that can help with the problem?

PS: I would also appreciated if you have any other solutions in your mind that I could implement. Any reply would be appreciated.

share|improve this question
This will show the bystanders at the scene : RegionPlot[ Or @@ (EuclideanDistance[#, {x, y}] <= 0.3 & /@ bystander), {x, 0, 7}, {y, 0, 7}]. – b.gatessucks Feb 2 at 13:39
Related discussion math.stackexchange.com/questions/135629/… – cormullion Feb 2 at 14:23
To have the bystanders represented by circles 30 cm in diameter you should use PlotMarkers -> {Graphics[{Opacity[0.1], Green, Disk[]}], 0.3/7} – m_goldberg Feb 2 at 15:36
3  
Back when I was in school, I did my homework myself. It's too bad the OP doesn't feel like thinking about this, because they can't learn much by copying code somebody else wrote. – Ted Ersek Feb 2 at 17:37
@ted Their professor may be reading this site, though! :) – cormullion Feb 2 at 20:20

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