The apartment is in the La Colonnade complex, which is near the intersection of Dix Highway and Northline Road. The victims have been identified as Courtney Durr and her son Samurai Das.
Barbaba Durr, Courtney's mother, tells FOX 2's Maurielle Lue she believes they were killed as early as Friday.
"We have been calling all weekend, her phone, and there was no answer, and we heard yesterday when a girl said that she's seen [the suspect] in my daughter's car and his head needed stitches," Durr says.
The man police have in custody is a recent acquaintance of Courtney's, and Durr says he was recently released from prison after serving a 10-year sentence. She says her daughter befriended the man, but they were not dating or romantically involved. She believes the man may have been jealous and had a different idea.
Neighbors tell Lue they are alarmed by what happened, but note several security issues recently. They say a gate stays open, there's no buzzer system in place and that some lights and security cameras may not work.
FOX 2 has attempted to speak with management at the apartment complex.
Southgate Police said in a news conference later Monday morning the suspect was arrested around 2:30 a.m. driving the victim's car.
This is a developing story. Stay with FOX 2 News for updates.