Masini was born on April 14, 1944, in Naples, Italy. At the age of 17, he relocated to the United States, eventually settling in Livingston, New Jersey. By 1966, Masini had his first encounter with law enforcement, resulting in a burglary conviction. Following his release, he took up various low-skilled labor jobs. He married a woman named Anna, and together they had two children. Masini owned two homes and worked as a handyman.

On November 24, 1991, Masini visited his 85-year-old aunt, Anna Masini, at her home. After a conversation over soft drinks, he attacked her with a knife, repeatedly stabbing her in the neck until she died. He then assaulted her body and fled. Anna's body was discovered on November 27, but Masini was not initially suspected, leaving the case unsolved for a year while he continued his travels.

On December 11, 1991, Masini entered the home of 79-year-old Angelina Ialeggio in East Orange. Ialeggio, a relative by marriage, was attacked similarly, with Masini stabbing and assaulting her before taking money and leaving.

Exactly a year after killing his aunt, on November 24, 1992, Masini visited the West Orange home of 81-year-old Michael Krieger and his 78-year-old wife, Betty. The couple, who had previously hired Masini for carpentry work, allowed him to do some housework. After discussing floor work, Masini attacked Michael with a letter opener. When Betty saw what had happened, he stabbed her in the back. 

The next day, their son reported their absence, leading to the discovery of their bodies and evidence of stolen items. With no signs of forced entry, the investigation focused on those close to the couple. Masini, known for working at their home, denied involvement. However, a bloody footprint at the scene matched a pair of specialized hiking boots he owned, leading to his arrest.

While Masini was in jail, authorities searched his home and found his wife wearing a ring that belonged to Angelina Ialeggio. Consequently, on December 23, Masini was charged with Ialeggio's murder and held on $1,000,000 bail. Detectives linked him to the unsolved murder of his aunt Anna in 1991. Superior Court Judge Joseph Falcon ordered Masini to provide blood, hair, and saliva samples.

Despite overwhelming evidence, Masini pleaded not guilty. The victims, all elderly and known to Masini, were killed on Wednesdays, stabbed in the neck, and the female victims were sexually assaulted. Two psychiatric evaluations confirmed his competence to stand trial. Eventually, Masini changed his plea, admitting to the murders. In exchange, the death penalty was removed, and charges of robbery and sexual assault were dropped, allowing him to avoid a trial.

During sentencing in April 1993, Masini expressed remorse to Judge Joseph Falcon, saying, "I need help. Please help me. I am very sorry. God forgive me." He was sentenced to life imprisonment with the possibility of parole after 60 years, making him eligible for parole on December 20, 2052.