Such killings weren't rare over the succeeding decades. The followers of Tiberius' brother Gaius died similarly, though the most famous example is the murder of Julius Caesar by Marcus Junius Brutus et al in 44BC.

Did any precedent exist at the time of Tiberius' murder?

To what extent were the suspensions of law later occasionally directed by the Senate and which came to be referred to as Senatus consultum ultimum considered to be in the same tradition?

Did the assassins that struck frequently from Caesar's time onwards and almost invariably after the death of Commodus ever refer to this senatorial habit?

Edit: The earlier office of dictator has been brought up in a comment now deleted. I'll add my intended reply here seeing as it clarifies what I'm asking about:

The continuities between extraordinary Senate powers during the late Republican period and the office of dictator occasionally instituted earlier are definite. OTOH, from Wikipedia:

As soon as the Dictator was appointed, he became the chief executive and commander-in-chief of the Republic. The regular magistrates – with the exception of the Tribune of the Plebs – became subject to the higher imperium of the Dictator. They continued to discharge the duties of their various offices under the Dictator, but they were no longer independent officers and were obliged to obey his orders in every circumstance. Failure to do so could result in the dictator forcing the magistrate out of office.

The superiority of the Dictator's power to that of the consuls consisted chiefly of greater independence from the Senate, more extensive power of punishment without a trial by the people, and complete immunity from being held accountable for his actions. However, what gave the dictator such great control over Rome was his lack of a colleague to counter him. Unlike the Consuls, who were required to cooperate with the Senate, the Dictator could act on his own authority without the Senate, though the Dictator would usually act in unison with the Senate all the same. There was no appeal from the sentence of the Dictator (unless the dictator changed his mind), and accordingly the lictors bore the axes in the fasces before them, even in the city, as a symbol of their absolute power over the lives of the citizens.

The Dictator's imperium granted him the powers to rule by decree and to change any Roman law as he saw fit, and these changes lasted as long as the Dictator remained in power.

Can you comment on the statement that "the regular magistrates – with the exception of the Tribune of the Plebs – became subject to the higher imperium of the Dictator"? Plebian Tribune was the position held by Tiberius Gracchus.

Could a dictator be appointed without the consent of the popular assembly, or even in defiance of it? Or does the sole authority of the Senate distinguish senatus consultum ultimum from earlier dictatorships?