Two civilians and one police officer died Friday in a shooting at a Colorado Springs Planned Parenthood clinic.

Shootings at abortion clinics are rare. But violence against clinics is not: There have been at least 73 successful attacks on American abortion clinics since 1997, according to the National Abortion Federation.

Forty of those acts of violence were arson attacks, including four in 2012. There have also been 20 attacks aimed at abortion providers themselves with different weapons, either shootings, stabbings, or acid attacks.

Most shootings, however, are typically perpetrated outside of the clinics themselves. The most recent shooting — the murder of Kansas abortion provider George Tiller — happened in the doctor's nearby church. In 1998, a New York abortion provider was shot and killed while sleeping in his home.

Violence against abortion clinics peaked in the late 1990s, as extreme anti-abortion groups like Operation Rescue advocated aggressively for attacks on clinics and providers. But it hasn't disappeared: In 2012 alone, there were four arson attacks on clinics in Florida, Wisconsin, and Georgia, and one failed attempt in Missouri.

The NAF database ends in 2012 — but more recently, the FBI has reported an uptick in abortion against clinics in the wake of sting videos taped inside Planned Parenthood locations, which purported to show the sale of fetal body parts.