TEL AVIV, Israel -- The death of yet another scientist working on Iran's burgeoning nuclear program Wednesday has started to make such killings look like a trend. But here in Israel, where the threat of an Iranian nuclear bomb feels most palpable, it has also invoked another great tradition: the winking, know-nothing denial.

"I understand there has been a problem with suicides among the scientists," one Tel Aviv-based military think-tanker said on the day of the killing, with a broad grin.

"Oh no," a top Knesset political adviser added later, eyes rolling, when asked about the scientist. "We know nothing about that."

It is a typical response in a country notoriously secretive about its military and espionage activities, even when its handiwork and capabilities seem obvious. After all, Israel still has not formally acknowledged possessing nuclear weapons, despite the established fact that it does.

The killing of Mostafa Ahmadi Roshan, a scientist at Iran's Natanz nuclear facility, on Wednesday morning while he was on his way to work was the latest in a string of highly suspicious incidents surrounding Iran's nuclear weapons program.

Since the incidents started about two years ago, four scientists have been killed and one gravely wounded, a highly sophisticated computer virus has ravaged the processors at Iran's central nuclear facility, and debilitating explosions have hit high-sensitivity military locations in the country.

In the latest incident at least, the Iranians have expressed little doubt as to who was culpable: Reuters quoted an official there as saying the bomb that killed Roshan was a magnetic device, similar to the ones that were used in previous assassinations, and was "the work of the Zionists" -- meaning, of course, Israel.

In The New York Times on Thursday, experts on Iran openly speculated that the killing has all the markings of an Israeli hit, perhaps even with American complicity.

"I often get asked when Israel might attack Iran," Patrick Clawson, the director of the Iran Security Initiative at the Washington Institute for Near East Policy, told the paper. "I say, 'Two years ago.'"

Meanwhile, Richard Silverstein, an American blogger who covers the Middle East, cited a "confidential Israeli source" as confirming that the hit was the work of the Mossad, Israel's spy service, together with a militant Iranian opposition group.

The White House and State Department, for their part, have both vehemently denied having anything to do with the killings.

"I want to categorically deny any United States involvement in any kind of act of violence inside Iran," Secretary of State Hillary Clinton said Wednesday during an appearance in Washington with the ruler of Qatar.

But Israelis, even officially, were more circumspect.

Speaking to the Washington Post, an Israeli government official said only, "It is not our policy to comment on this sort of speculation when it periodically arises."

Meanwhile, on his Facebook page, Yoav Mordechai, the spokesman for the Israel Defense Forces posted, "I don't know who took revenge on the Iranian scientist, but I am definitely not shedding a tear."

An IDF spokesman did not respond to The Huffington Post's request for comment.

It's not the first time. When an arms depot outside Tehran exploded last November, killing 17 members of the country's elite Revolutionary Guards, Israel's defense minister Ehud Barak told reporters that he had no idea what had happened, but added, "May there be more like it."

None of the think-tankers or political analysts who pepper the security think tanks of Tel Aviv are likely to have firsthand information of any covert operations, but Israeli involvement in the killing seems to almost be taken for granted here -- as is the great practice of outright denial.

"You could argue it's a clear modus operandi" for the Israeli spy services, Shlomo Brom, a retired IDF general and senior research associate at the Institute for National Security Studies in Tel Aviv, told HuffPost Thursday. Then he added, "But of course, I don't know anything."