Well, this is a bit too unspecific to win any prizes, but it is as comprehensive as you can get. The song title is "A Death Song" (appropriate huh??), words by William Morris, music Malcolm Lawson. Written to commemorate the killing of Alfred Linnell by the police at a   demonstration in 1887. The song sheet was sold to raise money for his family.
   And the relevant bit is the chorus:

Not one, not one
Nor thousands must they slay
But one and all
If they would dusk the day