Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
The mode in which the democracy dealt with the ancient criminal
jurisdiction of the comitia was characteristic. It had not been
properly abolished by Sulla, but practically the jury-commissions
on high treason and murder had superseded it,(5) and no rational
man could think of seriously re-establishing the old procedure
which long before Sulla had been thoroughly unpractical.
But as the idea of the sovereignty of the people appeared to require
a recognition at least in principle of the penal jurisdiction
of the burgesses, the tribune of the people Titus Labienus in 691
brought the old man, who thirty-eight years before had slain or was
alleged to have slain the tribune of the people Lucius Saturninus,(6)
before the same high court of criminal jurisdiction, by virtue of which,
if the annals reported truly, king Tullus had procured the acquittal
of the Horatius who had killed his sister.