Police in California are investigating claims a high school student mixed her cremated grandfather's ashes into homemade sugar cookies and shared them with several classmates.

Key points: Cookies that allegedly contained cremated human remains were shared with at least nine students

Cookies that allegedly contained cremated human remains were shared with at least nine students One classmate said he was "horrified" after "feeling it crunching in between your teeth"

One classmate said he was "horrified" after "feeling it crunching in between your teeth" Investigators said they were at a loss to identify a motive and were unlikely to lay charges

The student and a friend baked the cookies and shared them with at least nine classmates at their public charter high school near Sacramento on October 4, said Davis Police Lieutenant Paul Doroshov.

He said the Da Vinci Charter Academy students told some of their classmates that the cookies contained human ashes.

Investigators interviewed nine students who ate the biscuits, Lieutenant Doroshov said, adding that there were other supporting details that he declined to disclose that made the allegations credible.

Lieutenant Doroshov said the students were unlikely to be charged with a crime, even if one could be found that would apply.

A classmate who told local news outlet KCRA that he unknowingly took a bite of one of the sandy-textured cookies said he believed they contained human ashes.

"She had mentioned her grandpa's ashes before," classmate Andy Knox said.

He said the girl, who was not identified by authorities, had previously offered him some ashes if he swapped desks with another student in their class.

"I didn't believe her until she pulled out the urn," he said, "she told me there's a special ingredient in the cookie."

He said he became worried after taking one bite.

"I thought that she put drugs in it or something," the classmate said.

The girl then laughed, he said, and said the cookie contained her grandfather's ashes.

"And I was really, I was kind of horrified," he said.

"If you ever ate sand as a kid, you know, you can kind of feel it crunching in between your teeth. So, there was a little tiny bit of that.

Investigators said other students knew of the ashes before eating some of the cookies.

No motive identified

Lieutenant Doroshov said he and investigators were at a loss to identify a motive and that there was no public health risk.

"They're juveniles and it's not a heinous or serious crime," he said.

"I really don't think it fits into any crime section."

Investigators looked at an obscure law making it illegal to mishandle human remains, he said, but "this isn't what that law was intended to stop."

He said police would let the school handle the matter.

Principal Tyler Millsap said in a statement posted on Facebook and emailed to parents that the incident had "been particularly challenging and we have responded appropriately and in the most respectful and dignified way possible".

"Those who were involved are remorseful and this is now a personal family matter," Mr Millsap said.

AP/ABC