An 86-year-old man fatally shot his grandson, his grandson's girlfriend before shooting himself after a housing dispute ended badly, a law enforcement source said, Fox 4 News reported Saturday.

According to authorities, police were trying to sort out what led the old man - identified as Heriberto Pagan - to drive from his Brooklyn home to the Staten Island home of his daughter Friday. But what happened when he got there took a turn for the worse as he shot two people prior to shooting himself.

A law enforcement source revealed that investigators are currently looking into the possibility of a housing dispute.

The grandson was allegedly "trying to take over" the Staten Island home with his girlfriend when the 86-year-old man came.

Pagan "wasn't appreciative of the way" his own daughter was being treated by the couple said the law enforcement source, adding that it was not clear whether Pagan's daughter was at the scene when the shooting happened.

Reports said police found the New York man with a gunshot wound on his head outside his car Friday evening just a couple of blocks from where the shootings happened. Pagan was rushed to the hospital in critical condition, but reportedly died Saturday morning.

Inside the Staten Island home vicinity, authorities found the body of Pagan's 47-year-old grandson, critically injured with a gunshot wound to the head.

Pagan's grandson has not been identified as of late.

Meanwhile, the grandson's girlfriend - identified as 28-year-old Clarita Christina Huerta, was found inside the house. She was shot in the head and was pronounced dead at the hospital.

"This is like a nightmare," John Rina, a neighbor of Pagan's daughter, told CNN affiliate WCBS.

Authorities believed Pagan shot his grandson when the latter approached the house; he shot Huerta inside before finally exiting the vicinity, only to fatally shoot himself after driving a few blocks from the scene of murder.

"I just heard a man screaming 'help me, help me,'" another neighbor told WCBS.

Police said a 4-month-old boy was found unharmed inside the home. The baby was placed in the care of child welfare authorities.