At a campaign stop at a diner in Greenville, South Carolina, Republican presidential candidate Rick Santorum said the U.S. should not have condemned the killing of Iranian nuclear scientist Mostafa Ahmadi Roshan. He was killed last week after bombs attached to his car by passing motorcyclists exploded. Santorum believes the administration’s approach does not reflect a hard line on stopping Iran’s nuclear weapons program.

According to the AP, he said: “Our country condemned it. My feeling is we should have kept our mouth shut.”

Responding to a question in Greenville, he said he supports missile strikes to stop its nuclear program, if Iran refuses to submit to inspections.

“If these are people who are developing a weapon to be used to either destroy the state of Israel or to spread terror — a reign of terror — around the world, we shouldn’t be sitting on the sidelines and letting it happen,” he said. “They cannot have a nuclear weapon, because you, in Greenville, will not be safe.”

The Obama administration took several opportunities to deny involvement in the attack. National Security Council spokesman Tommy Vietor said: “The United States had absolutely nothing to do with this.”

At a press conference with the Qatari Prime Minister Wednesday, Secretary of State Hillary Rodham Clinton said:

“I want to categorically deny any United States involvement in any kind of act of violence inside Iran. We believe that there has to be an understanding between Iran, its neighbors, and the international community that finds a way forward for it to end its provocative behavior, end its search for nuclear weapons, and rejoin the international community and be a productive member of it.”

Secretary of Defense Leon Panetta also vehemently denied U.S. involvement in the killing. AFP reports:

During a meeting with soldiers at a Texas military base, Panetta said the United States was “not involved in any way, in any way with regards to the assassination that took place there.”

“I’m not sure who was involved. We have some ideas as to who might be involved. But we don’t know exactly who was involved,” he added.

The administration also condemned the killing – which Santorum took issue with – and went so far as to call the victim “innocent.” State Department Spokeswoman Victoria Nuland on Wednesday said:

“We’ve seen the reports of the death of the Iranian scientist as a result of an apparent bombing. We condemn any assassination or attack on an innocent person, and we express our sympathies to the family.”

As Santorum suggested, the words coming out of Washington raise questions about the extent of President Obama’s commitment to ensuring Iran does not develop a nuclear weapons capability. If Iran is developing weapons of mass destruction, combined with the Islamic Republic’s statements about destroying the State of Israel, do nuclear scientists then fall into the terrorist category acceptable for targeted killing? Is a focused covert war preferable and less costly than all out bombing?

The Telegraph explored the issue: Is it moral to kill Iran’s nuclear scientists? Though it’s unknown who exactly was behind the assassination, The Telegraph wrote:

The Israelis believe that anyone who knowingly participates in developing weapons of mass destruction or terrorism should be aware that these are not risk-free activities. Iranian scientists know full well that electronic switches are used in nuclear triggers, and that enriching uranium beyond a certain percentage is not for the production of medical isotopes. And they accept the considerable financial rewards involved. If there are questions about the morality of killing such men, there are questions about the morality of their work in the first place…

They work for a regime that has explicitly threatened Israel (and by implication many ambient Palestinians) with such a weapon.

Speculation continues to abound regarding who may have carried out the attack. TIME magazine believes it was the Mossad, while Israeli President Shimon Peres says to the best of his knowledge, Israel was not behind it.

Israel’s military spokesman, Brig. Gen. Yoav Mordechai while stressing he didn’t know who was behind the killing, wrote on his Facebook page: “I will definitely not shed a tear for him.”

Iranian Foreign Minister Ali Akbar Salehi says his country has “credible” evidence it was the work of the CIA. Iran also sent a letter to the British Foreign Office claiming the MI6 was also involved.

In the cloak and dagger world of international espionage, it may be years before anyone reveals how the hit occurred.