(CBS) TERRE HAUTE, Ind. -- Four people charged in a 9-year-old Indiana boy’s starvation death now face additional charges after an autopsy found methamphetamine in his system.

Cameron Hoopingarner’s two guardians and two other people originally were charged with neglect of a dependent resulting in death and other counts.  Hoopingarner was blind and weighed less than 15 pounds when officers found him Feb. 21 at a home near Fontanet, 60 miles west of Indianapolis, Vigo County Sheriff Greg Ewing said.

The officers were responding to a 911 call about a child in cardiac arrest. The boy was pronounced dead at a hospital.

State police and sheriff’s officials arrested four people who live at the home, including the child’s two guardians, Hubert A. Kraemer, 56, and 53-year-old Robin Lee Kraemer, who are charged with neglect of a dependent resulting in death and neglect of a dependent. If convicted of neglect leading to death, they could each face up to 40 years in prison.

Their son Chad Allen Kraemer, 33, and his girlfriend Sarah Beth Travioli, 30, are charged with neglect of a dependent resulting in death, neglect of a dependent and failure to report child neglect.

But prosecutors filed additional drug-related charges against them Monday after test results found the boy, who had cerebral palsy, had meth in his system.

Forensic pathologist Dr. Roland Kohr tells the Tribune-Star the drug entered the boy’s system as it was used by the people who “were supposed to be caring for him.”

An autopsy determined he died of starvation. The case has been ruled a homicide, reports the IndyStar.  According to court documents obtained by the paper, the boy’s skin appeared to stretch over his bones.

“In my 26 years in this office, the pictures that I saw of Cameron and his condition were terrible, beyond terrible,” Ewing said.