Around 3:30 AM on Friday morning, the Planned Parenthood health center in Pullman, Washington was set on fire.

As The Spokesman-Review reported, the fire burned for three hours, damaging support beams and compromising the building’s structural integrity. No one was inside at the time. By nightfall, the Pullman Fire Department and the Inland Northwest Joint Terrorism Task Force determined that the suspicious fire was indeed arson. The task force—which includes the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives—will be investigating the crime further.

On Aug. 22, less than two weeks before the Pullman clinic was set ablaze, the Idaho-based Selkirk Pro-Life Alliance sponsored a large anti-abortion protest at the nearby Spokane clinic. Over 500 protestors gathered there, repeating allegations made by David Daleiden’s that Planned Parenthood “sells baby parts” and calling for the organization to be defunded.

But at this early stage of the investigation, the most frightening thought about the crime isn’t the possibility that the arson was directly motivated by the anti-abortion protests stirred up by the CMP’s undercover video campaign, it’s the thought that this is simply be business as usual.

According to statistics gathered by the National Abortion Federation (NAF), there have been 186 arsons committed against abortion providers since 1976—an average of over 4 per year. There have also been approximately 40 bombings over the same time period. In fact, a Planned Parenthood clinic located an hour and a half north of the Pullman health center was bombed in 1996, leading to the sentencing of four Idaho men who belonged to an antigovernment militia.

On one hand, then, it is easy to speculate that this latest arson could have been provoked by the same CMP viral videos that prompted a dozen or more state investigations into Planned Parenthood, and that provided Senate Republicans with the motive for an unsuccessful attempt to defund the women’s health provider early last month.

But on the other hand, this could have simply been the Pullman center’s time. Abortion clinics get burned. It is shocking, yes, but also, horrifically unsurprising.

In a statement to the media, Planned Parenthood regional CEO Karl Eastlund called the arson “an appalling act of violence towards Planned Parenthood, but unfortunately a predictable ripple effect from the false and incendiary attacks that fuel violence from extremists.”

The history of anti-abortion arson is a long and sordid one. Below are a few cases from the last few years alone.

In April 2012, Francis Grady started a fire in a Wisconsin Planned Parenthood clinic. In court, he admitted to the crime but also claimed that he wanted to “release the souls of the children” through fire and “give them their last rites.” For this reason, Grady argued, he couldn’t technically be considered an arsonist. He was found guilty anyway.

On New Year’s Day 2012, a homeless Florida man, Bobby Joe Rogers, threw a Molotov cocktail at a Pensacola abortion provider. As the AP reported, Rogers “told detectives he had been living in a parking lot near the clinic and decided to set the fire because he was upset that abortions were performed there.”

“Thank God it’s blowed,” he told a reporter from a local news station, referring to the protestors who regularly picketed the clinic as “saints.”

The clinic Rogers burned had previously been bombed multiple times, in addition to being the site of the 1994 murder of Dr. John Britton, who was shot in the head with a 12-gauge shotgun by the now-executed Paul Jennings Hill.

In 2009, two young men, Sergio Baca and Chad Altman, pled guilty to the 2007 firebombing Dr. Curtis Boyd’s clinic in New Mexico. The plea agreement (PDF) reveals Baca’s disturbing motive: His ex-girlfriend was planning to receive an abortion at the clinic.

“Upon hearing this, Baca became extremely upset,” the plea deal reads. “Shortly thereafter, [he] went to Dr. Boyd’s office … and retrieved abortion pamphlets and literature. Baca then sent those items to his former girlfriend via the U.S. mail.”

The next night, he and Altman drove to the clinic, broke the windows, poured gasoline into Dr. Boyd’s office, lit the building on fire, and drove away. Baca’s ex-girlfriend received the pamphlets in the mail the following day.

Many other recent cases of arson at abortion providers are still open, including the case of two Georgia clinics that caught fire in 2012. As Reuters reported, there were patients inside one of the clinics when the fire started but, fortunately, no one was injured.

Fire is not the only tool that violent anti-abortion extremists use but it is one of their favorites. There have also been several acts of vandalism, anthrax threats, and acid attacks at abortion providers since the 1970s.

As the investigation into this latest arson gets underway, public attention to the Center for Medical Progress will inevitably be renewed. The organization has continued to release videos alleging that Planned Parenthood profits from fetal tissue donation, furthering widespread pro-life outrage even as state investigations into the organization come up empty-handed.

In a statement to The Daily Beast, CMP founder David Daleiden said, “The Center for Medical Progress does not support vigilante violence against abortion providers, and I would just echo what Planned Parenthood said in that we're grateful no one was injured.”Daleiden added that his “thoughts and prayers” are with some of the people at Planned Parenthood whom he still considers friends.

Daleiden’s stance against “vigilante violence” was not always shared by Cheryl Sullenger, the senior policy adviser for Operation Rescue.

Operation Rescue is an extreme anti-abortion group that, as its president and current CMP board member Troy Newman previously told The Daily Beast, provides “advice, consulting, [and] funds” to the CMP. Sullenger spent two years in federal prison from 1988 to 1990 after plotting to bomb a San Diego abortion provider. She has since “openly denounced violence as a means to stop abortion,” according to her bio.

In a previous statement to the press, Planned Parenthood Executive Vice President Dawn Laguens accused the CMP of having “troubling ties with violent extremists,” referring to the Operation Rescue ties.

When CNN anchor Alisyn Camerota pressed Daleiden about Operation Rescue in early August, Daleiden responded, “You’d have to talk to Troy [Newman] specifically about the full history of Operation Rescue and some of those details.”

On August 31, the Selkirk Pro-Life Alliance—which organized the late August protest in front of the Spokane clinic—posted a Facebook status about “Emmett,” an aborted fetus from the CMP videos that some pro-life activists have given a name.

“Emmett you will have justice,” the status reads. “Your short little life sparked the flames that will burn down the abortion industry and save the lives and souls of many babies and their mothers.”

There is no evidence at this point to suggest that the group was involved in the arson. Planned Parenthood has seen the status and a source within the organization told The Daily Beast that they have forwarded it to the authorities, who are taking it seriously but no investigation into the group has yet been confirmed.

As an unfortunate choice of words, the status would still reveal how tense this debate has become. The fire at the Pullman clinic was put out after three hours but the flames of controversy will roar for a while longer yet.

Correction 9/8/15 4:30 PM: A previous version of this article misreported the location of the Selkirk Pro-Life Alliance’s protest against Planned Parenthood. The protest took place at the Spokane clinic, not the Pullman clinic.