U.S. Ambassador to South Korea Mark Lippert on Thursday gave a statement to the police about last week’s attack by a radical activist, as investigators continue to zero in on the motive of the attacker.

In his statement, the envoy gave details of the attack, which occurred during a seminar at Sejong Arts Center in Seoul last Thursday. Lippert testified at his home for about 1 1/2 hours after being visited by an investigator and a translator.

The authorities are piecing together the assailant’s whereabouts from the day he received an invitation to the event, police said. The case will be referred to prosecutors no later than Friday, they added.

The suspect, who is facing three charges including attempted murder for his attack on the envoy, has been denying the charges, claiming that he did not intend to kill the ambassador, the investigators said.

Meanwhile, a local news outlet reported Thursday that U.S. investigators have been stationed at the Korean police headquarters to monitor the investigation, causing a debate over “judicial sovereignty.”

According to No Cut News, U.S. Federal Bureau of Investigation agents have been staying at the Seoul Metropolitan Police Agency since the assault took place.

The U.S. authorities had reportedly offered to conduct a joint probe but the Korean police declined in consideration of judicial matters, the report added.

“Allowing the FBI agents to stay at the office seems overly accommodating,” Rep. Shin Kyoung-min of New Politics Alliance for Democracy was quoted as saying. “The authorities are supposed to determine the need for U.S. support based on whether the case is an act of terrorism or assault. In this case, it’s very unlikely that it’s the former.”

The Korean police officials claimed the U.S. agents were here only for necessary information-sharing as the two parties cooperate actively.

Korean National Police University professor Park Cheong-sun agreed, saying, “While the jurisdiction of the case is within Korea’s authority, foreign agents can be dispatched upon mutual agreement because of the distinctiveness of the case.”

By Lee Hyun-jeong (rene@heraldcorp.com)