CHELTENHAM TOWNSHIP, Pa. (CBS) - Cheltenham police say an eight-year-old boy will undergo a mental health evaluation after allegedly stabbing his great-grandmother in the back inside their Melrose Park home over the weekend.

Police were called to Jeanes Hospital on Sunday evening where they say the 54-year-old woman told them her great-grandson used a kitchen knife to stab her three times in the back (see previous story). She was treated and released.

Authorities say the young boy was also allowed to go back home Monday evening.

Cheltenham police Chief John Norris says the investigation is continuing, but he says there was no argument between the boy and the woman and they’re not sure yet what sparked the attack.

“He said he heard voices,” said Chief Norris.

Police say when they asked the boy why he did it, he responded by telling investigators about a video game that he had just watched right before the incident.

Jericka Duncan Reports …

“What was interesting was that he was watching a video game before this occurred, and it was one of those violent video games that you see around,” said Chief Norris.

Norris says the boy may be suffering from some type of mental illness, but says he has a good record at school and there have been no police calls to the home, in the 7400 block of Fourth Avenue.

The police chief says the assault apparently just came out of the blue.

Reported by Brad Segall, KYW Newsradio 1060.