Who Killed Germanicus

I'm bored so I thought I would start a series on who killed Germanicus. Not that anyone I know really cares but it will fill up blog space and maybe I'll learn something in the process. I'll add theories as to who killed him when I get around to it. Here is his basic bio:

* Born: 24 May 15 B.C.
* Birthplace: Rome
* Died: 10 October 19 A.D. (possibly poisoned)
* Best Known As: Commander of Roman legions on the Rhine

Germanicus, the adopted son of the Emperor Tiberius, was named Consul of Rome at age 27. The next year he was sent north to lead Rome's legions against the rugged tribes along the Rhine River. Germanicus succeeded (more or less) and put down a rebellion of Roman troops while he was at it. He returned to Rome a hero, but died less than two years later under mysterious circumstances; some suggest he was killed on orders from a jealous Tiberius or from Tiberius's scheming mother Livia. Most of what we know about Germanicus comes from the historian Tacitus, who generally cast Germanicus as virtuous and Tiberius as the bad guy.

Germanicus was the father of a later emperor, the notorious Caligula, and the brother of Caligula's successor Claudius.
Source: Answer.com