Paul continues to speak.

## they themselves know ##

The non-believing Jews at Jerusalem.

## beat those ##

"Arranged to have them punished by a whipping"

## every synagogue ##

Paul sought out any jewish believers who attended any synagogue around Jerusalem.

##  the blood of Stephen...was spilled ##

this is an expression for brutally beating a person until they are dead. (See:  [[rc://en/ta/man/translate/figs-idiom]])