Let me guess: none of the victims and no one in the area was armed and able to defend themselves or others.
Thank you Mayor Stalin
The murderer was targeting a single individual. He waited for a former coworker to leave the office, came up to him and shot him in the head at point blank range.
He then put the weapon inside his suit jacket and calmly walked away, hoping that he could disappear into the rush hour crowd without getting apprehended (a couple of years ago a similar event happened at rush hour and the shooter was lost in the crowd).
But a couple of construction workers saw him and started to pursue him and the commotion had already brought police to the vicinity.
The construction workers pointed him out to the cops, the murderer pulled out his weapon and there was a short street battle.
The only dead were the murderer and his victim - and even if his victim had been armed, he would have had no chance.
None of the usual cliches apply to this situation.