EVEN before the news was official, it filtered out — unofficially — to Wall Street.


On a trading floor in Midtown Manhattan, the squawk boxes were set to relay a market-moving bulletin at 10 a.m. This was the news: An analyst at the investment house was raising his assessment of Amkor Technology, a big name in computer chips.


But it was only 9:30, and Amkor’s share price was already rising. By the time the announcement came, it was up 4 percent. “It was clear that my research had been leaked,” the analyst, Ted Parmigiani, recalls.


But leaked how, and by whom? To Mr. Parmigiani, there was only one explanation: someone inside his own research department had tipped off the firm’s traders, as well as some fast-money hedge funds.


Nearly seven years later, the events of that June day — and countless others like it, up and down Wall Street — still rankle him. The fallout effectively ended his career. The firm he worked for, Lehman Brothers, was eventually undone by greed and hubris, its spectacular collapse in September 2008 a symbol of an age of financial excess.


Against the sweeping morality tale of Lehman, the story of one analyst may seem trivial. But it’s a story central to post-crisis Wall Street, and to the regulators watching over it. Federal authorities today are trumpeting efforts to root out insider trading, and they’ve caught some big fish. Yet many on Wall Street suspect that the sort of chicanery that Mr. Parmigiani says he witnessed at Lehman may be as common as ever.


More worrying, from his perspective, is that he provided the Securities and Exchange Commission with evidence pointing to frequent insider trading involving analyst research at Lehman, but the S.E.C. ultimately did not bring a case. Mr. Parmigiani spent two and a half years giving information to the S.E.C. He produced materials indicating that Lehman sales representatives were tipped off to upcoming research changes; data showing suspicious trades in dozens of stocks; organizational charts and floor plans showing that some Lehman executives who were part of the research department were located near sales and trading desks. These departments are supposed to be separated.


With that ammunition, the S.E.C. opened an investigation, case HO-10864. Officials told him that his evidence was credible.


Then the case died. And after Lehman’s collapse its employees have scattered across Wall Street.


Since the financial crisis, the S.E.C. has spent a lot of time and money trying to plug leaks. In a case worthy of “Law & Order,” prosecutors used wiretaps to ensnare Raj Rajaratnam, the billionaire Galleon hedge fund manager whose web of tipsters stretched from Wall Street to some of the mightiest corporations in the land. For his crimes, Mr. Rajaratnam, whom prosecutors called “the modern face of illegal insider trading,” was sentenced last October to 11 years in prison.


Mr. Rajaratnam’s conviction, in the largest insider-trading scandal in a generation, handed a much-needed win to the beleaguered S.E.C. Only two years earlier, the commission had been lambasted for missing glaring evidence of Bernard L. Madoff’s vast Ponzi scheme.


But Mr. Parmigiani and others suspect that the P.R. of the Galleon case glosses over risks that insider trading can and does occur regularly at many Wall Street firms. In their view, it has become institutionalized. The flow of information between a firm’s analysts, its traders and its clients — a lucrative heads-up on stock upgrades and downgrades, for instance — can bolster trading profits, brokerage commissions and, ultimately, Wall Street paydays. Those in the know can get rich before the rest of us know what happened.


“Prosecutors say insider trading won’t be tolerated, that this is justice,” Mr. Parmigiani says of the Galleon case. “But they refuse to acknowledge that their widespread net has a very big hole in it.”


What exactly happened at Lehman? Mr. Parmigiani says traders there were routinely advised of changes in analysts’ company ratings before those changes were made public. That way, Lehman could profit on subsequent market moves. Here is how he describes it: First, research officials tipped off the traders; then Lehman’s proprietary trading desk, which cast bets with the firm’s own money, positioned itself accordingly. Lehman salespeople also alerted favored hedge funds. Only later, he says, were ratings changes made public.


Blowing the whistle on any big corporation, as Mr. Parmigiani tried to do in the case of Lehman, is almost always perilous. Shortly after noting the suspicious trading in Amkor, Mr. Parmigiani says, he was fired for not being a team player. He has since been unable to find work on Wall Street.


John Nester, a spokesman for the S.E.C., said it conducted a careful, thorough investigation of Mr. Parmigiani’s allegations.