From the linked story:
At 6:57PM EST on December 16, 2012, Duncan wrote to Emanuel in a message titled “CT shootings.”
Duncan asked the Chicago mayor, “What are your thoughts?”
Five minutes later, Emanuel responded, “Go for a vote this week before it fades. Tap peoples emotion. Make it simple assault weapons.”
Duncan responded immediately, “Yup- thanks.”
“When I did brady bill and assault weapons for clinton we always made it simple. Criminals or war weapons,” Emanuel said in the email to Duncan.
“Gun show loophole?” Duncan responded. “Database? Cop-killer bullets? Too complicated?”he said.
“Cop killer maybe,” Emanuel responded. “The other no.”
The exchange ended when Duncan concluded with, “Got it.”