The guy that assassinated President McKinley was tried, convicted, and executed on the order of six weeks after McKinley died (~week after being shot).
We are facing increasingly serious problems with violent crimes and major factors driving this are the gansta culture and the fact that gangs use minor age children to commit many crimes because they are subject to the liberal juvenile legal system and get their records clean slated when they turn 18
These gang members grow up accustomed to commiting serious crimes that are glorified in their gang culture and have no serious punishment consequences because even rape and attempted murder get expunged from their records when they turn 18.
A few swift executions would act as a deterrent