This was Luke's overt ploy.
He knew that Amanda Waller didn't dare protect these informants, because what she had asked these gangsters to do couldn't be revealed.
From the evidence he gave, there was no doubt that the gang bigshots wouldn't be able to escape.
Secondly, most of the blame fell on the gang members under Amanda's control.
These people were basically the backbone of their gangs.
With some support from Amanda, they got rid of a few competitors, made a small fortune, and sat in key positions in the gang, which made it easier for them to do things for Amanda.
They weren't officials, and didn't even know Amanda's face or identity.
Thanks to the evidence which Luke provided, these dozen or so people were all charged with serious felonies.
He used NYPD and New York's D.A. to nail them aboveboard, and didn't need to lift a finger at all to kill them himself.