The Inspector-General of Police said the suspect was picked up in the north of the country last week.
"We believe he is relevant to the ongoing investigation into the abduction of Koh.
"Let us investigate the case thoroughly," he told a press conference in Bukit Aman after launching a blood donation programme here on Wednesday.
Previously, police detained a man in Ampang who demanded a ransom for allegedly kidnapping Koh. However, it turned out to be a hoax and the man has since been charged in court.
Khalid also warned certain parties not to make baseless allegations in connection with Koh's abduction.
"We are not sitting on the case. We have never stopped investigating his abduction and efforts to locate him are ongoing," he said.
Khalid said police were also investigating reports that Koh was attempting to proselytise Muslims, and determining if this had any connection to his abduction.
"We have to investigate as a police report has been made," he said.
On claims that the authorities were connected to Koh's abduction, the IGP sternly warned activists or other parties against spinning the facts.
"If you don't have any evidence or proof, don't make allegations. It is a very serious allegation," he said.