The origins of the pentagram are actually tied to the orbit of Venus. This is from an astronomy site:
"Look down on the plane of the Solar System from above the Earth. Track the Earth so it always appears directly below you, but don’t turn along with it. With the passage of each year, you will see the Sun go around the Earth. As the Sun goes around the Earth 8 times, Venus goes around the Sun 13 times, and traces out the pretty curve shown here.
It’s called the
pentagram of Venus, because it has 5 ‘lobes’ where Venus makes its closest approach to Earth. At each closest approach, Venus move
backwards compared to its usual motion across the sky: this is called
retrograde motion."
This is a lot easier to visualize with graphics - just google it.
Venus of course is known as the 'Morning Star'. Lucifer is called the 'bright morning star'. Therefore Venus=Satan=Venus' orbit=Pentagram.
We also have the apple. If you cut an apple crossways you will see a natural 5 shaped star. Satan of course is also linked to the apple from the garden. (though I don't believe eating an apple was THE sin in the garden, but that's a whole different topic) This also links Satan to the Pentagram.
Police often times find pentagrams painted on the ground at sites where animals or people have been ritually murdered. So yes, they use them.
And the illuminati often times schedules events according to the orbit of Venus.