Etan Patz: Possible blood stain found on basement wall, search suspended for the day

A suspicious stain on the wall of a basement is being tested by authorities who have continued the search for Etan Patz, who has been missing since 1979.

According to Fox News, when investigators sprayed Luminol on the basement wall, "an organic substance" was detected that could possibly be blood. The stain has been removed from the basement — of which about 50 percent has been dug up — and will be tested further.

The stain, which has been described as a spot on the wall, was found Saturday, the third day the New York Police Department was digging up the basement in question, reported Reuters. The space was used as a workshop by handyman Othniel Miller — now a person of interest in the case — at the time of Patz's disappearance. Miller has not been charged with a crime and has cooperated with police since the investigation started 33 years ago.

More from GlobalPost: Etan Patz: Basement searched in boy's 1979 disappearance (VIDEO)

The search that turned up the stain has had to be suspended until tomorrow morning, with FBI spokesman Peter Donald citing "operational reasons" as the cause for the abrupt stop, according to CNN.

"I don't want to get into what those reasons were," Donald said. "We'll be back in the morning."

Patz, just six years old at the time of his disappearance, was one of the first missing children in the US to have his picture printed on milk cartons. According to Reuters, he was formally declared dead in 2001.

The 33-year-old case was recently reopened when a cadaver-sniffing dog sensed something at the SoHo basement where the stain was found. Investigators were initially looking for clothes and human remains.