(Mr. Ma, now in a federal prison in Brooklyn, declined through his lawyer, Don Buchwald, to be interviewed.)

The government does not believe that Mr. Ma was ever formally associated with a tong, but he would have known the major players — like Clifford Wong, leader of the Tung On tong, or Paul Lai, president of the Tsung Tsin Association, who once served on an advisory panel for Gov. Mario M. Cuomo and even attended the wedding of the governor’s daughter. (Both men were eventually convicted on racketeering charges.)

Mr. Ma was instead a member of the 14K triad, federal agents say, a Hong Kong group founded more than 60 years ago by 14 leaders of the Kuomintang nationalist party. Based in Queens, he oversaw gambling parlors, a luxury car-theft ring, extortion rackets and an immigrant smuggling operation. By his own admission, though, his most profitable business was always heroin — and that, of course, was why he had sent his killers to Toronto.

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In the morning, their getaway car was gone.

Perhaps someone had stolen it. The men, at any rate, had a backup plan. They had stolen license plates from another car, according to court papers, and they put these on the minivan they had driven from New York. They dropped the women at a park and drove past Seafood Alliance. In the afternoon, when the coast was clear, Mr. Wah pulled the van into a parking spot. Mr. Cai and Mr. Nguyen walked toward the door. It was locked, so Mr. Nguyen fired a few shots, shattering the glass. He stepped inside. Mr. Cai followed.

Waiting in the van, Mr. Nagatsuka heard more shots. Many, many more. Years later, at the murder trial of Bing Yi Chen, he testified as to what happened next:

Mr. Wah “started putting the minivan into reverse, started pulling away from the parking lot. Once we were driving away, we see Paul Cai and Luyen coming out, running fast. Along the way, Paul Cai disassembled his handgun, threw the handgun parts to an empty lot on the right side. We were following at a slow pace along with Luyen and Paul Cai. There was a Home Depot nearby. We went to the back of it. That’s where the plan was to meet, in the back of the Home Depot. Once we turned the corner to the Home Depot, we start hearing the siren.”

They found Christina and Salina and hurried the 80 miles back to Niagara Falls. The next day, they saw news coverage of the murders on TV: two bodies being carted off by the police. They returned to New York City and to Mr. Ma’s apartment. There, court papers say, they apologized to Mr. Chen.

They had escaped unscathed. But, on reading the morning papers, they realized they had killed the wrong two men.