Word that a federal grand jury in Boston is looking into recent mutual fund scandals highlights the difficult question of just how deeply criminal prosecutors could or should be involved in a matterthat has traditionally been the purview of the civil justice system.

Securities law experts said this week that the grand jury, first reported in The Boston Globe and confirmed by a source with knowledge of the matter, was no surprise given the volume of material referred to prosecutors by state and federal regulators on the civil side. But there is no guarantee that criminal charges will follow.

The uncertainty is partly due to the delicate legal ground beneath prosecutors, experts say.

Late trading, or executing orders at an old price after the window has closed, is clearly illegal. (Unlike stocks, mutual funds price just once a day.)

But market timing, the quick trading in and out of funds that has been at the heart of much of the scandal, is not illegal per se, though regulators have alleged it amounts to civil fraud if practiced by companies that have promised their customers they don’t allow it.

One company, Security Trust Co., was shut down after New York Attorney General Eliot Spitzer brought criminal charges accusing three former executives of grand larceny and other charges for helping hedge funds engage in short-term trading, which skims profits from long-term investors.

And on Thursday, Spitzer, along with the SEC, announced a $250 million settlement from Alliance Capital Management for allowing a hedge fund to extensively market time its funds.

The arrangement with Alliance allowed Daniel Calugar, the owner and president of Security Brokerage Inc. in Las Vegas, to make $64 million in profits from timing trades in the funds, even as fund shareholders lost money, the SEC said.

In a deal that caused friction between the two regulators, the New York attorney general also brokered a separate deal forcing Alliance to cut its fees to holders by $350 million over five years.

The payment is the largest ever by a mutual fund adviser, the SEC said. And experts said the size of the payment set a precedent and likely would spur other companies to settle.

That could be good for regulators, because while several experts said egregious market-timing abuses could rise to the necessary threshold for deliberate criminal intent, that could be a tough sell to a jury.

“Market timing alone I think is a very difficult and unattractive criminal case,” said Jeffrey Stone, a former federal prosecutor who now heads the white-collar defense practice at McDermott Will & Emery in Chicago. While the Department of Justice is under extraordinary pressure to show it is pursuing wrongdoers, prosecutors “like to bring strong cases” they are confident of winning, he said.

“They’re going to look for the most egregious examples they can find,” Stone said. “A pure market timing cases does not rise to that level.”

The broader issue is to what degree criminal prosecutors should be involved at all. For years, securities law has largely been the purview of the more flexible civil system, with regulators like the Securities and Exchange Commission wringing fines and behavioral changes from wrongdoers and criminal charges being reserved for the most serious cases.

“Overall, this is part of a broader trend we’ve seen over the last two or three years to criminalize the enforcement of federal securities law,” said Stephen Crimmins, a former deputy chief litigation counsel at the SEC now in private practice at Pepper Hamilton in Washington, D.C. “Coming down heavy on a small number of people isn’t going to offer the opportunity for restructuring a portion of the securities industry that the interests of the general public may require.”

Many lawyers also believe that, for better or worse, federal prosecutors are under pressure to show the flag in what has become a turf battle involving state and federal authorities. The sharp criticism endured by the SEC for falling behind state regulators was widely noted.

“There is pressure on the Department of Justice not to be marginalized,” Stone said.

Spitzer, who cracked open the mutual fund scandal in September, has been aggressive in pursuing fund companies, naming more than a handful of companies as having made questionable trades with one hedge fund charged, and bringing civil or criminal charges against about a half dozen individuals. Spitzer has been critical of the SEC for not discovering the trading abuses and not being aggressive in rooting out violators and punishing them.

Spitzer and the SEC traded jabs Thursday as they jointly announced a $600 million settlement with Alliance Capital Management for allowing a hedge fund to market time its funds.

But at an SEC news conference, Stephen M. Cutler, director of the SEC Division of Enforcement, downplayed the disagreement with Spitzer, saying both agencies had the same objectives even if “we don’t agree on every point.

Samantha Martin, a spokeswoman for the U.S. Attorney’s Office in Boston, said she could neither confirm nor deny any investigation. Traditionally, the U.S. Attorney’s Office for the Southern District of New York has led securities industry investigations, but it is not known whether that office has convened a grand jury.