Why did the mad king kill Ned's father?

Related questions

1. Is Jon Snow Eddard Stark's son?
2. How many sons did rhaegar have?
3. Why did littlefinger have Jon Arryn killed?
4. Were Lyanna Stark and rhaegar married?
5. Do the Dragons know Jon Snow is a Targaryen?
6. Why does Ned Stark say Jon Snow is his son?
7. Who married rhaegar and Lyanna?

Tags

1. #father
2. #landing
3. #stark
4. #rickard
5. #sister
6. #south
7. #rebellion
8. #imprisoned
9. #brandon
10. #demand
11. #treason
12. #entourage
13. #justice
14. #lyanna
15. #aerys