CNN US

It's April 4, 1968, and the Rev. Martin Luther King Jr. steps outside his room at the Lorraine Motel in Memphis, Tennessee, and leans over the balcony.

As the investigation continues into why a female shooter opened fire at YouTube headquarters, data show that it's rare for women to carry out such shootings -- making Tuesday's incident unusual.

The shooting in San Bruno, California, at YouTube's headquarters was, in some respects, just another case of gun violence.