Del Ponte is one of the investigators on the United Nations fact-finding mission investigating war crimes in Syria.
Last month, Del Ponte told Swiss-Italian television she had "strong, concrete suspicions" that the Syrian rebels used poison gas against civilians. Citing testimony from survivors in hospitals outside Syria, Del Ponte said, "This was used on the part of the opposition, the rebels, not by the government authorities."
Del Ponte is familiar with politicised war crimes investigations. She was removed from her post as prosecutor at the UN Tribunal for Rwanda after a US diplomat warned her to cease investigation of war crimes by Paul Kagame's Rwandan Patriotic Front, a US and UK ally.
In its statement on Syria, the White House noted that it has been "working urgently with our partners and allies as well as individuals inside Syria, including the Syrian opposition, to procure, share, and evaluate information". The Syrian opposition, though, seems like a less reliable source than an international war crimes prosecutor.
In justifying its escalation, the US Government has stated that the use of chemical weapons "violates international norms and crosses clear red lines that have existed within the international community for decades" - but so does rape, torture, forced conscription of child soldiers, and the killing of unarmed civilians or captured combatants.
So why now?
The administration also concedes that its change in approach is "particularly urgent right now" because Iran and Syria's Lebanese militia ally, Hizbollah, have increased their own involvement. That support has driven significant military gains by the Syrian Government in recent weeks.
Iran has responded to US intent to supply weapons by pledging to supply Assad with 4000 Iranian Revolutionary Guards.
Another issue undermining the US chemical weapons justification is the comparatively marginal impact of chemical weapons use. The US alleges chemical weapons have killed 100-150 people. That's about 0.1 per cent of the almost 93,000 deaths the UN cites since the start of the Syrian uprising.
It brings into question a sensitive principle called the "responsibility to protect" (R2P) via military means, and what triggers it. The Obama administration's red line appears to assert a responsibility to militarily intervene and protect when it is strategically convenient, rather than when it is merited by the scale of ongoing suffering.
The Syrian war is being fought on multiple levels. Within Syria, and in the region, the conflict has turned into a Shia Islam versus Sunni Islam conflict. Bashar al Assad's Shia-backed minority government, Iran, an increasingly Shia-dominated Iraq and Hizbollah are fighting a Sunni majority in Syria, supported by Saudi Arabia, Qatar, Jordan, Egypt and other North African governments.
At the international level, Nato powers, particularly the US, the UK and France, have lined up with the Sunnis against Syria's long time ally, Russia, which enjoys diplomatic support from China.
The international stakes are enormous. The Syrian and Iranian governments have been Russia's two strong allies in the region. Russia has a defence agreement with Syria and a naval base on Syria's Mediterranean Coast.
Regime change would geographically isolate Hizbollah from critical Iranian support, significantly weakening Iran's influence in the region - a huge loss for Russia, and a gain for the US and Israel.
Indeed, armed foreign intervention in situations such as Syria advances US interests.
However, they may not be able to stop weapons from going into the hands of extremists, or maintain influence over a potential post-Assad government. The most effective anti-Assad militia, the al Nusra Front, is also an affiliate of al-Qaeda in Iraq.
By escalating the conflict, the US most likely presumes it can tip the military balance against Assad and negotiate a favourable regime change from a position of strength.
Russia, which recently confirmed sale of anti-aircraft missile systems to Assad, appears wary of this possibility. Russia, therefore, appears prepared to match each escalating move.
By escalating the conflict, both sides deepen it, diminishing potential for peaceful resolution. UN Secretary General Ban Ki Moon recently stated that there is no military solution to Syria's conflict.
Nothing excuses the Syrian Government's killing of peaceful protesters. However, the US implicitly endorsed the arming of regime opponents by Saudi Arabia and Qatar. That elevated instability from abhorrent suppression of protesters to an armed conflict of far greater devastation to Syrians.
The Russians view the use of humanitarian justification as selectively deployed by the US in Syria, but not where US interests require protecting autocratic and repressive allies, such as in Yemen.
Russia often cites what appears to be its, and China's, own red line: Libya. In Libya the UN Security Council imposed a no-fly zone that was used by Nato to achieve regime change through continued bombing of Libya long after the country's air force was no more.
Humanitarian intervention allows, and potentially encourages, cynical governments to foment instability in autocratic states where they have an interest in regime change.
Once that regime engages in abuses, the option is then available to intervene.
Russia and China are not providing weapons to opposition elements in Yemen, but in time, in similar situations, they could.
Syria demonstrates Russia and China's growing global clout. China's economy is due to surpass that of the US in 2016. It need not withhold its veto when it views UN Security Council resolutions as facilitating Western aggression, particularly when acting alongside Russia.
In Syria, the US is setting a precedent that allows the drawing of convenient red lines in the future, by the US or other global powers. Perhaps these red lines arbitrarily drawn up by one government need a red line drawn through them.
An earlier version of this article appeared in the Atlantic:
Chris Mahony is deputy director of the NZ Centre for Human Rights Law, Policy and Practice at the University of Auckland.
