An illegal immigrant and key witness in the fatal hit-and-run of a Massachusetts man is believed to have fled the country, MyFoxBoston.com reports.

U.S. Immigration and Customs Enforcement (ICE) reportedly told the station that it wasn't their responsibility to keep track of 20-year-old Luis Acosta, who removed his GPS monitoring bracelet on Oct. 1 and is feared to have left the country.

Acosta's cellphone was reportedly found at John. F. Kennedy Airport in New York, and his name appeared on a flight manifest to Ecuador.

Acosta was riding in the passenger seat when another illegal immigrant, Nicholas Guaman, allegedly hit and killed 23-year-old Matthew Denice in Milford, Mass.

Milford Police Chief Tom O'Loughlin told the station that ICE did not alert local police that Acosta's GPS bracelet was cut until six days later.

"It really begs the question: Why put the bracelet on to begin with?" O'Loughlin said. "They never notified us. We called them, they told us six days later that the bracelet was cut up. We didn't see an ICE agent until 10 days after the bracelet was cut off."

ICE, however, claims procedures were properly followed, according to the station. ICE reportedly told MyFoxBoston.com that local jurisdictions have the responsibility to keep track of possible witnesses.

Denice's family called the crime a "murder," and said ICE's failure to immediately notify local law enforcement is "mind-boggling," according to the station.

Guaman, 34, was arrested in August after his vehicle struck Denice, who was on a motorcycle, according to police. Guaman's pickup truck had allegedly dragged the young man's body a quarter-mile.

Guaman is accused of negligent vehicular homicide while driving under the influence of liquor, leaving the scene of an accident involving personal injury and death, possession of an open container of alcohol in a vehicle and unlicensed driving, among other charges.

"We hope and expect in a Federal investigation will soon reveal exactly how and why Luis Acosta was able to flee the United States," the family said in a statement released to MyFoxBoston.com. "We were informed that the DA notified ICE in early September that Acosta was a critical eyewitness to a homicide."

"ICE knew our family was depending on them to ensure justice would be served for Matthew," the family said.

Denice had just graduated from Framingham State University with a computer degree.

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Immigration officials: Not our job to keep track of murder witness: MyFoxBOSTON.com