Finally realizing they had been caught red-handed, Saudi Arabia decided to own up to the deed.

On Thursday, a Saudi prosecutor said that the murder of dissident journalist Jamal Khashoggi was being investigated as a premeditated attack. That leaves Trump with the difficult task of figuring out just how to respond when a U.S.-based journalist winds up dead and dismembered after a trip to his consulate en route to getting married. Whatever Washington settles on as an appropriate response, one thing is clear: it must not act alone.

Trump is not alone as a leader of a country outraged by the drip of gruesome details released by Turkish officials, including a recording of the murder shared with CIA Director Gina Haspel on her trip to Turkey.

Indeed, several U.S. allies around the world are mulling their own responses and trying to figure out just where they stand when it comes to cutting arms sales, imposing sanctions and even calling out the Saudi Crown Prince Mohammad bin Salman.

Already Germany has suspended arms sales to the kingdom, and Canada has convened a series of emergency response meetings to formulate the countries response. Like the U.S., both countries have cashed in on arms deals with Saudi Arabia but have remained critical of the kingdom's track record on human rights.

This should be a key moment for Trump to demonstrate that not only does the U.S. stand for human rights, but that it does so alongside its allies. This would bolster America's image internationally where the country raised eyebrows by pulling out of the United Nations Human Rights Council.

More importantly, any sanctions that the U.S. settles for will be far more effective combined with similar efforts from allies. After all, the U.S. is not the only country keen to profit from selling arms to Riyadh.

Of course, not every ally will be so quick to come out strongly against Saudi Arabia and, particularly, the powerful crown prince.

Israel, looking to build an alliance against Iran, views Saudi Arabia as a key member of the alliance. The United Arab Emirates likewise has heavily invested in its partnership with the kingdom and the leadership of Mohammad bin Salman.

Even if those countries would be unlikely to join in a unified effort to hold the kingdom accountable, Washington would be wise to first consult with their leaders so as not to blindside them and complicate existing relationships.

To be clear, the U.S. must respond to Saudi Arabia for both the murder and the kingdoms subsequent lies. But Washington would do well to recognize the value of international alliances in challenging Saudi Arabia and ensure that Washington has a coordinated, or at least informed, response.