Honolulu police arrested the 19-year-old grandson of 70-year-old woman stabbed Friday morning in Kaimuki.
It happened at around 1:15 a.m. from an apartment complex on Waialae Avenue near Kapahulu Avenue.
Neighbors say the Charles "Kelii" Amoy may have shown signs of behavioral issues.
The woman was taken to the hospital in critical condition.
Honolulu police arrested Amoy at 6 p.m. Friday at the University of Hawaii at Manoa, where he was a student.
Police opened an attempted murder investigation.