A family friend called police after finding the bodies of 20-year-old Robert Regazzi and his 53-year-old mother, Cheryl Regazzi, inside their Gillies Street home in Clifton around 4:30 p.m. Saturday.
The deaths remained under investigation on Sunday, but Passaic County authorities say it appears that the pair died in a murder-suicide.
A motive for the shooting remains unclear.
Officials say Cheryl Regazzi was shot once, but further details on her death were not immediately disclosed. And while they believe her son purposely overdosed, the drug he took won't be known until toxicology test are completed, a process that could take several weeks.
The Regazzis were last seen on Thursday night, when they took their trash cans to the curb for pickup on Friday. But the cans then remained in the street until Saturday morning, when a neighbor brought them back to the curb.
(The Associated Press contributed to this report.)