Seoul (CNN) Beginning more than three decades ago, 10 women died in a spate of killings in the same South Korean city.

For years, authorities were stumped by what local media has called the worst serial murder case in the country's modern history.

But in a press briefing Thursday, South Korean police said they believed they had identified the man behind at least three of the killings which took place in Hwaseong, a city south of Seoul, between 1986 and 1991.

The alleged suspect, who police did not name, is in his 50s and is already in prison where he is serving a life sentence, according to CNN affiliate KBS . A police official for the Gyeonggi Nambu Provincial Police Agency confirmed to CNN that the man is in his 50s, but declined to provide any further details.

But the suspect won't face charges over the killings, as South Korea's statute of limitations on the cases ran out in 2006.

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