It happened around 11:25 Monday night.
Action News was there as first responders and Bensalem Police tried to sort out a disturbing scene in Longmeadow Apartments on the 3000 block of Bristol Road.
Investigators say inside a home, they found 30-year-old Koustantinos Yiambilis, his 59-year-old mother Karen and a portable generator which was on and spreading deadly fumes.
"We saw them bringing Karen out and we saw everything unfold from that point on and it was obviously just shocking," said Jessica Shaffery, family friend.
Karen was rushed to Aria Torresdale Hospital where she was pronounced dead.
Her son survived but police arrested the man accusing him of intentionally killing his mother.
"It's alarming, the way it was done. Not only that but the potential risk it put the other residents," said Sgt. Andrew Aninsman, Bensalem Police.
The residents who live in the same building were briefly evacuated.
Residents also told Action News that the incident was a suicide pact between the mother and son. Both lost their jobs and were going through financial and medical problems.
"In my opinion they did this together because they had nothing left. They lost everything," said one neighbor.
The generator found in the home belonged to a neighbor and friend, who doesn't want to be identified. The neighbor says Karen borrowed it hours before.
"I'm angry that I was used and so upset that I will never see her again and they shouldn't blame it on him because he's got some major mental problems," said the neighbor.
Bensalem police wouldn't confirm the suicide allegations but those who have known Koustantinos for years say he loved his mother.
"They just had a lot going on and they didn't have the resources that they need for themselves and I think that it was just too much for them to handle at that point," said Shaffery.
Police say two dogs were also pulled from the apartment but they survived the fumes.
Koustantinos, who was also taken to the hospital for treatment, was arraigned Tuesday and is being detained with no bail. Once released from the hospital, he will be taken to Bucks County Prison.