The years after the death of Drusus are filled with more trials. Nineteen trials are reported in Dio and Tacitus and there may have been other in the missing parts of Tacitus’ account from AD 29 onwards.

1. Vibius Serenus was condemned for the use of violence while proconsul in Spain (AD 23) (Annales 4.13).
2. Gaius Silius, a prominent general, was accused of treason and corruption while in Germany. His wife, Sosia, was also tried. The trial was led by the consul, Varro, who was an old enemy. He offered little defence and killed himself. Sosia was banished  (AD 24) (Annales 4.18-19; 20).
3. Calpurnius Piso was accused of treason. When that charge did not stick, a number of others were offered. He died (naturally?) before a verdict was reached (AD 24) (Annales 4.21).
4. Cassius Severus, who was already in exile, was summoned to Rome, tried again and exiled to a smaller island (AD 24) (Annales 4.21).
5. Plautius Silvanus, a praetor, threw his wife out of a window. He claimed that he was sleep-walking. Tiberius himself inspected the room and saw evidence of a fight. He was invited to commit suicide, which he did (AD 24) (Annales 4.22). 
6. Numantina, Silvanus’ divorced wife, was accused of having driven him mad by poison or sorcery. She was acquitted (AD 24) (Annales 4.22). It is interesting to wonder who brought the case; perhaps friends of Silvanus seeking some revenge?
7. Vibius Serenus, also already an exile [see 1], was summoned back to Rome to face accusations of treason levelled by his son, also Vibius Serenus. He was accused with a Caecilius Cornutus, who promptly killed himself before suffering the trial. The accusations then focused on Gnaius Lentulus and Seius Tubero, two grandees of the Tiberian senate. These were untouchable and the cases against them failed. Tiberius had the slaves of the elder Serenus tortured, but they provided no consistent evidence. At this point, public opinion turned against the younger man. Having his father tried for treason was interpreted by the crowd as attempted parricide. The younger Serenus fled Rome, but Tiberius had him hauled back from Ravenna and forced him to continue the trial. The elder Serenus was found once more guilty and was once more exiled. The senators, however, sought to prevent his son receiving the rewards due to those who informed: clearly, some were less than impressed. Tiberius insisted, however, that the security of the state depended on informers and they needed their rewards (Annales 4.28-29; 30) (AD 24).
8. Gaius Cominius was convicted of writing scandalous verses about Tiberius. He was forgiven on the intercession of his brother, a senator (AD 24) (Annales 4.31).
9. Publius Suilius was accused of corruption and exiled (AD 24) (Annales 4.31).
10. The historian Cremutius Cordus was accused of having written in favour of Brutus and Cassius. Tacitus gives him a long speech defending the rights of historians. He killed himself before the verdict was announced and his works were burnt (AD 25) (Annales 4.34-35).
11. Sextus Marius was accused by Calpurnius Salvianus. Salvianus misjudged the political mood and was exiled (AD 25) (Annales 4.36).
12. The young Vibius Serenus appeared once more with accusations against Fonteius Capito. The charges were proven fictitious, but Serenus was under the protection of the emperor and escaped punishment (AD 25) (Annales 4.36).
13. Votienus Montanus was accused of circulating insulting stories regarding Tiberius. The prosecutor made the unfortunate error of loudly repeating each accusation, thus giving them maximum publicity. Tiberius was apparently enraged. Votienus was found guily of maiestas (AD 25) (Annales 4.42).
14. A woman named Aquila was found guilt of adultery and exiled (AD 25) (Annales 4.42).
15. Claudia Pulchra, a cousin of Agrippina, was charged with adultery and an attempt to poison the emperor. Agrippina intervened on her behalf. Pulchra and her supposed lover, Furnius, were found guilty. Tiberius publicly praised the prosecution (AD 26) (Annales 4.52).
16. Quintilius Varus was tried, but the senate stopped the prosecution to seek the advice of the emperor, who was by now resident on Capri (AD 27) (Annales 4.66).
17. Titius Sabinus, a close friend of Agrippina and her sons, was lured into political conversations in which he bewailed their misfortunes and attacked Sejanus and Tiberius. He was condemned by letter from Tiberius and hurried off (Annales 4. 68–70). He was murdered in prison and his body thrown into the Tiber. In an oddity, it is reported that his dog followed him to prison and into the river (Dio, 58.1) (AD 28).
18. Asinius Gallus, a close friend of Germanicus and one of the most prominent figures in the senate, was accused of treason. Tiberius had him imprisoned, but not brought to trial (Dio, 58.2).
19. Syriacus, a friend of Gallus, was executed, supposedly solely on the grounds of his friendship. (Dio, 58.2).

The point about these trials is their repetitious nature. We cannot know the politics behind most of them, but since the accused were members of the political elite, these were all political trials.

Some of them seem related to Sejanus, but most were in-fighting among senators. Some trials were the furtherance of old enmities, but others, such as the prosecutions of Vibius Serenus and Titius Sabinus were within families or between friends. Who could be trusted in such an environment? Given that the informer was handsomely rewarded if the case went with him, wealth and any hint of unpopularity with the emperor or Sejanus made people vulnerable. Increasingly, friendship with Agrippina or Germanicus marked individuals for attack. We should also remember that the price of losing one of these trials was at best exile and at worst death.

The atmosphere among the Roman elite must have been poisonous.

We cannot attribute all the trials to a narrative of the fall of Agrippina and her sons, but the fighting in the senate and inexorable rise of Sejanus was building to a situation in which their removal was possible.