In February, a Salvadoran member of the MS-13 gang, 17 at the time, allegedly lured Vanessa Argueta, 19, and her 2-year-old son, Diego, to an industrial park and shot them in the head, the New York Daily News reported.
Judge Joseph Bianco approved murder in aid of racketeering charges against the unnamed defendant, now 18.
"It is hard to imagine a more compelling case for transfer to adult status," Bianco wrote in his ruling. "The juvenile justice system, including the limited sentencing options ... is simply ill-equipped and woefully insufficient under the circumstances."
Argueta had been dating another MS-13 member, court papers said. After breaking up with him, she asked members of the rival 18th Street Gang, based in Los Angeles, to beat him up, the report said.
The ex told the alleged killer, authorities say. After the crime, they fled to El Salvador and were arrested in April at the Miami airport when they tried to return, court papers show.