The earliest use of it that I am aware of is from The Scourge of Corruption. Or a crafty Knaue needs no Broker. Printed for Henry Gosson and William Houlmes, 1615). However, that does not relate to juries.
The earliest use of it relating to a jury that I am aware of is from The Muses looking-glasse. Printed by Leonard Lichfield for Francis Bowman, 1638), by the poet and playwright Thomas Randolph (1605-1635).
If you have an earlier source, I would be fascinated to see it.