Updated

The U.S. Drug Enforcement Administration is investigating how its agents forgot about a college student who was picked up during a sweep and left him in a holding cell for five days without food, water or access to a toilet.

Daniel Chong, 24, was never arrested, was not going to be charged with a crime and should have been released, said a law enforcement official who was briefed on the DEA case.

The official, who spoke on the condition of anonymity to discuss the investigation, said DEA investigators are trying to figure why Chong was forgotten while other suspects were released.

While he sat in the cell, Chong said he drank his own urine to survive and that he bit into his glasses to break them and tried to use a shard to scratch "Sorry Mom" into his arm. His account was published in a story Tuesday in U-T San Diego.

DEA spokeswoman Amy Roderick said he was accidentally left there. The agency has not commented on Chong's claim that he was without basic necessities for days.

The engineering student at University of California, San Diego, was swept up as one of nine suspects in an April 21 drug raid that netted 18,000 ecstasy pills, other drugs and weapons.