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Poor visibility in a man-made lake's toxic waters is hampering the search for a victim of a suspected serial killer, Cyprus authorities said Monday.

Investigators believe a suitcase at the bottom of the lake contains the remains of one of seven foreign women and girls that a Cypriot army captain has confessed to killing.

But it has been slow going for a robotic camera being used in the search at the bottom of the lake that was part of a now-defunct copper pyrite mine, fire chief Marcos Trangolas told The Associated Press.

He said visibility is just mere inches in the murky waters, but authorities will carry on the search until at least two more suitcases believed to also contain human remains are found.

He said a sonar device able to map the lake bottom in great detail will also be deployed in the coming days.

The 35-year-old suspect said he put the bodies of three of his victims — believed to be a Romanian mother and daughter, and a Filipino woman — in suitcases and dumped them in the lake.

A suitcase containing the remains of an adult woman and weighed down by a concrete block was retrieved from the lake Sunday.

Authorities have so far recovered the bodies of four of the suspect's alleged victims over what authorities believe was a 30-month time span.

Only one victim has been positively identified — 38 year-old Mary Rose Tiburcio whose bound body was found down a flooded shaft that was part of the same copper mine.

Police said they were tipped off about the body's discovery April 14, touching off an investigation that led to the suspect through his exchange of online messages with Tiburcio with whom he had a six-month relationship.

Investigators told a court that during his arrest, the suspect tried but failed to swallow a mobile telephone SIM card.

The suspect initially admitted to only two killings, but last week admitted to killing seven women — four of them from the Philippines, two from Romania and one who authorities believe to be a Nepalese woman.

Tiburcio's 6-year-old daughter Sierra is also believed to be among the victims and authorities are searching for her body in a reservoir about 12 kilometers (7.5 miles) west of the man-made lake.