Did the U.S. directly assist the Saudi-led coalition aerial bombing of a funeral in Sanaa, Yemen this weekend, reported to have killed over 140 people and injured as many as 600? A renowned combat aircraft engineer and former Pentagon official, Pierre Sprey, says the evidence suggests the U.S. did exactly that.

In the ‘60s, Sprey was one of Robert S. McNamera’s whiz kids at the Pentagon, where he served as an engineer developing the military’s next generation of combat aircraft. As a chief architect of the Air Force’s F-16 (its predecessor, the F-15, is the most common combat aircraft in the Saudi arsenal), Sprey revolutionized the fighter jet by prioritizing agility over what he saw as unnecessary bells and whistles. His F-16 remains widely used by the Air Force to this day, even outperforming the latest generation of fighter jet.

As Sprey explained to AlterNet, “If that Saudi fighter was based at the main Saudi base near Riyadh, Prince Sultan airbase, then it was almost certainly refueled by USAF [U.S. Air Force] tankers.” Though there is an airbase located close enough to Yemen to not require refueling, King Khaled airbase, Sprey told AlterNet, “I doubt they are stationing very many fighters there these days, given that the Houthis [rebel group that overthrew Yemen’s government in 2014-2015 following protests against a deeply unpopular fuel subsidy cut] have successfully hit that base with Scud missiles on at east one occasion (and could readily overrun it on the ground, given the dismal performance of Saudi ground units).”

In an interview with the Huffington Post, Sprey estimated that even if the Saudis’ F-15s launched from a base bordering Yemen, they would have only five to 15 minutes of time over the closest rebel territory. Alternatively, if the jets were to target the rebel cities in the southwest of Yemen, they would have only five minutes over those cities. This is hardly the kind of time necessary for the strafing runs of a bombing operation.

Former Army Sgt. Maj. Michael Adams, a Special Forces veteran with numerous classified combat deployments, agrees that the Saudis wouldn’t risk leaving valuable fighter jets on a vulnerable border, telling AlterNet, “If the Saudis had aircraft stationed anywhere near the border of Yemen, the Houthis would definitely attack it. They’ve already attacked into Saudi territory and they could either attack it using rocket launchers or artillery attacks or they could do hit-and-run terrorist type attacks on the air base and destroy the aircraft on the air base. So it would be completely ridiculous from a military strategic standpoint for the Saudis to station aircraft anywhere near the border of Yemen.”

Still, how hard could it be to secure a single location?

“Nothing’s secure against any type of suicide attack,” Adams explained. “Also, the Houthis are proving now that they have the capability to launch long-range attacks. They’ve launched, within the last week, long-range missile attacks into Saudi Arabia in addition to the attacks that they allegedly launched on U.S. naval ships.”

“The Houthis are pretty well trained—they could also launch a reasonably sophisticated special operations type of attack. Any airfield is a large area: you can’t build a completely impregnable defense around an airfield. It’s just not possible.”

But how could Saudia Arabia, one of the richest countries in the region, not manage to secure an airbase against one of the poorest countries, Yemen?

“Combat is not just about money, it’s about capabilities. You can be the richest country in the world and get your ass kicked depending on the tactics that are used against you. The obvious example is the United States and Vietnam. Same thing in Afghanistan with the United States.”

When AlterNet asked U.S. Air Force spokesman Shane Huff, he conceded that the U.S. refueled coalition fighters the weekend of the bombing—including the day after the bombing—but denied that USAF fueled any aircraft on the day of the bombing. When asked why the U.S., which typically refuels coalition aircraft, would provide fuel that weekend but not the day of the bombing, Huff replied, “I do not know the answer to that question.”

Asked if the aircraft involved in the Sanaa funeral bombing launched from an airbase bordering Yemen, Huff told AlterNet, “I must refer you to the Saudi Defense Forces on that question.”

Sprey told us that USAF handles “the vast majority of refueling” for coalition fighters. According to Huff, the U.S. has offloaded fuel to 5,730 receiving coalition aircraft since April of 2015.

The U.S.’ role in the bombing may even go beyond refueling: a photo has emerged allegedly showing the ordnance dropped on the funeral, a Mark 82 bomb (the label printed in English). The U.S. announced a contract for the production of this ordnance for Saudi Arabia, just weeks before the bombing. Even Ken Roth, executive director of Human Rights Watch, later tweeted the potentially incriminating photo; this may come as a surprise given HRW’s well-documented congeniality to Washington.

The photo shows the remnant of a U.S.-supplied guidance kit for a U.S.-supplied Mark 82 bomb. On Nov. 13, 2015, the U.S. government announced a $1.29 billion sale to Saudi Arabia of over 19,000 bombs, including 8,020 Mark 82 bombs and 3,400 JDAM tail kits. Both are manufactured by American corporations: the Mark 82s by General Dynamics and the JDAM kit by Boeing.

U.S. involvement in Yemen isn’t limited to fueling coalition jets and providing munitions: it recently deployed Special Operations troops to Yemen. The Pentagon stated that this will be “short-term”; however, a national security journalist for the Washington Post recently tweeted that the troops are “not likely to go anywhere,” citing a defense official on background.

Though the Yemen offensive is widely attributed to a “U.S.-backed, Saudi-led military coalition,” even this may be too generous in light of the extent of U.S.’ fueling, arms and troop support, none of which appear contingent on Saudi’s respect for the laws of war. The Saudi funeral bombing bears a grim resemblance to U.S. airstrikes, having bombed at least eight wedding parties since 2001. The fact that senior Houthi political and military officials were in attendance at the funeral, many of whom were killed, suggests a possible motive for the bombing.

Following the funeral bombing, the U.N. Secretary-General has called for an independent investigation into rights abuses and other crimes in Yemen. With about half of Yemen’s population going hungry according to U.N. figures, this conflict threatens to turn Yemen into an irrevocable humanitarian catastrophe.