Five deaths in the last month have sparked outrage in Nigeria, with protests erupting across the city by women activists fearing a rise in killings targeting suspected sex workers.
Police had already arrested one suspect but said in a statement on Twitter that another suspect had been arrested on Thursday morning.
"The notorious serial killer, Gracious David West was today... arrested by the Police in Rivers," it said, releasing a video confession from the suspect.
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The suspect was also a member of a cult they said.
"He has since made useful statements to the police," they added, announcing that a news conference would be held in Port Harcourt on Friday.
In a statement on Tuesday, police said the murders were thought to have had a ritualistic element.
"After the killings, white cloth material is rolled on the victims' necks or waists. So, there is an element of cultism in all the killings in the hotels that have taken place," Rivers Police Commissioner, Mustapha Dandaura said.
"The serial killer normally drugs his victims and thereafter, he strangles them," he added.
In recent days, women took to the streets of Port Hartcourt in a series of protests calling for better police protection.
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Outrage at the killings and the police response spilt over on to social media after police told protesters that women should abandon prostitution to avoid being targeted.
"We must go back to try to educate them [women] and discourage them from going into prostitution because that is how they fall victim to these crimes," deputy commissioner of police, Chuks Enwonwu told demonstrators, according to local reports.
Protesters and activists condemned the police response, saying all women were vulnerable to the rising attacks.
Prostitution is illegal in Nigeria, and police have enforced restrictions on hotels in the city, forcing hotel owners to install closed-circuit cameras to monitor activity or face closure.
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