Girls aren't pulling the triggers? The "modern" school shooting was invented by a girl in San Diego when a Brenda Spencer shot up an elementary school:

https://en.wikipedia.org/wiki/Cleveland_Elementary_School_sh...

There was even a pop song written about the incident.

And more recently, Tafsheen Malik, shot up a San Bernadino workplace along with her husband.

And a woman along with her husband went on a shooting rampage in Vegas in 2014. http://abcnews.go.com/US/las-vegas-cop-killers-husband-wife-...

Women were persons of interest in the most recent Vegas shooting, and the wife of the Pulse gunman was arrested in connection with the murders (http://abcnews.go.com/US/wife-pulse-nightclub-gunman-omar-ma...).

Women can and do pick up guns and murder.