[They did pat him down before trying to put the cuffs on him..]
There have been a number of instances where the suspect was searched, cuffed, produced a gun and killed the arresting officer. You could say the cops involved were remiss, but they are still dead. Not all criminals are dumb. And cops don’t always encounter criminals when they are fresh and alert, at the beginning of their shift.
They pat him down around 9 minutes into the video. They try to cuff him around 29 minutes.