Kenneth T. Robinson exits federal court in Newark, N.J., on Monday. Robinson, a mortgage broker, pleaded guilty today to his role in an insider trading scheme spanning 17 years. (Steve Hockstein/BLOOMBERG)

As the middleman in an alleged insider trading conspiracy, Kenneth T. Robinson took care to stay under the government’s radar.

He conveyed information about corporate deals from a Washington lawyer to a New York trader using pay phones and prepaid cellphones, the government says. To collect his share of the profits, the government says, he sometimes met the trader in Atlantic City, where gambling could provide an alibi for cash withdrawals. And, by serving as the go-between for the lawyer who was the source of the tips and the trader who acted on them, the government says, he made it less likely that law enforcement would connect the dots.

But in 2009 and again last year, he let his guard down and placed trades on his own, leaving himself more vulnerable to detection. That lapse gave investigators a big break, and it ultimately led them to his door, a source familiar with the investigation said Monday.

Based in part on Robinson’s cooperation, the Justice Department and the Securities and Exchange Commission last week charged trader Garrett D. Bauer and corporate lawyer Matthew H. Kluger with collaborating in a 17-year scheme that netted more than $32 million since 2006 alone.

Robinson, 45, previously identified in court papers as “Coconspirator 1,” was unmasked as the alleged middleman Monday, when he pleaded guilty to securities fraud and conspiracy.

The charges could bring up to 45 years in prison and fines of more than $10 million, but under a plea agreement, the government is recommending a prison sentence of 70 to 87 months.

Robinson, a Long Island resident, was once registered as a trader but worked primarily in the mortgage business, the government said.

Robinson and Bauer were already on the government’s radar when Robinson invited closer scrutiny by trading on his own, the source said, speaking on the condition of anonymity to discuss details not spelled out in court papers.

But it was Robinson who exposed Kluger as the origin of the inside information, the source said. Kluger worked for some of the nation’s most prominent corporate law firms: Cravath Swaine & Moore; Skadden, Arps, Slate, Meagher & Flom; Fried, Frank, Harris, Shriver & Jacobson, and most recently Wilson Sonsini Goodrich & Rosati, where until weeks ago he worked in the Washington office.

The FBI and the Internal Revenue Service visited Robinson’s home early last month, and soon conversations between Robinson and his alleged partners were being recorded with Robinson’s consent.

The government quoted extensively from the recordings in the charges against Bauer and Kluger.

“If they start looking at me and look at my bank records and all that other stuff . . . it could get ugly,” Kluger said in a March 17 call, according to federal officials.

“I am waiting for the FBI to ride into my apartment. And I am on edge all night thinking that they’re coming in,” Bauer allegedly said in a March 18 call. “I mean, the fact is we did something wrong.”

In one of the calls, Kluger allegedly mused about the possibility that Robinson would “flip.” But Robinson had already flipped.

Federal officials said the scheme began in the 1990s, when Kluger was working as a summer associate at Cravath and realized he had access to inside information about upcoming mergers and acquisitions. He turned to his friend Robinson, who agreed to find people who would buy and sell stocks based on that information, the government said, and Robinson recruited Bauer.

Kluger gave Robinson tips that Robinson passed to Bauer, and Bauer then shared the proceeds with the others, the government said.

According to the U.S. attorney’s office for New Jersey, which is prosecuting the criminal case, Robinson admitted Monday that he personally placed trades in at least two instances: the acquisition of 3Com by Hewlett Packard, announced in November 2009, and the purchase of McAfee by Intel, announced in August 2010.

As early as 1999, a brokerage firm accused Bauer of insider trading. In a private lawsuit, TFM Investment Group alleged that Bauer had “non-public material information” when he bought options in advance of a 1998 deal involving Clorox. A judge dismissed the suit, explaining that TFM did not say where Bauer supposedly got the inside information. The suit was previously reported by the New York Times.

Bauer was released Monday on a $4 million bond, said Rebekah Carmichael, a spokeswoman for the U.S. attorney’s office. The conditions include having his mother live with him and act as a custodian, Carmichael said.

Kluger was being held while awaiting transfer to New Jersey.

Kluger, 50, is a son of Richard Kluger, a Pulitzer Prize-winning author and former executive editor of the publishing house Simon & Schuster. Richard Kluger’s books include “Simple Justice,” about the landmark Supreme Court case Brown v. Board of Education, and “Ashes to Ashes,” about the tobacco industry.

Richard Kluger said Monday that he and his wife were shocked by the charges and “knew nothing about any of this.”