TOKYO -- A South Korean ex-police chief has been arrested in the attempted cover-up of the torture death of a student activist last year, but the nearly fatal torturing of a teen-age suspect last week has raised questions about the extent to which South Korean police have changed their methods despite recent democratization.

Kang Min Chang, 55, former director of the National Police Headquarters, was arrested last weekend for his alleged role in trying to conceal the torture of Park Chong Chul, a student activist whose death one year ago provided the key rallying point for South Korean opposition forces last year.

Kang, charged with negligence in performing his duties, is the highest-ranking law enforcement officer to be arrested in South Korea since 1960, when a police chief was arrested for the brutal suppression of a student revolt.

Kang's arrest, prompted by recent testimony from a doctor who conducted the autopsy of the 21-year-old student's body, peels back a third layer of a cover-up that has been unraveling since Park's death on Jan. 14, 1987.

The Korea Herald editorialized Tuesday that Kang's arrest demonstrates South Korea's commitment to "equality before the law." But the newspaper then noted that a teen-age murder suspect is now in an apparently irreversible coma after being severely beaten by police officers in a police station basement.

"Torture is one of the darkest spots in the tradition of our law enforcement system," the newspaper said. "It has been very slow in dying out despite popular outcries and legal safeguards against it."

South Korea last month elected a new president, Roh Tae Woo, ushering in what officials said would be a new democratic era for a nation long ruled by military-installed, authoritarian governments. Opposition politicians have said that a key test for Roh, who is leader of the ruling party, will be his commitment to curbing the nation's vast and intrusive law enforcement and intelligence agencies.

South Korean officials have always claimed that torture in the nation's jails is rare. Opposition politicians and outside human rights groups, however, have documented many cases.

In the wake of the latest torture case, the incumbent national police chief, Kwon Pok Kyong, this week directed police across the nation to respect the rights of suspects in custody, "no matter how serious the nature of their alleged crimes."

The latest case involved a 17-year-old identified as Myong No Yol, suspected of raping and murdering a high school girl in December. Myong, his hands and legs tied, was severely beaten over the course of four days, from Jan. 9 to Jan. 12, in the basement of the Suwon police station south of Seoul as police attempted to extract a confession, investigators said.

Despite his frequent vomiting, police did not take him to the hospital until he lapsed into a coma, according to news reports. Doctors found water in his lungs, likely indicating water torture, the accounts said. Three officers have been charged in the case and in an alleged attempt to cover it up.

The Park Chong Chul case shocked the nation one year ago, galvanized the opposition to President Chun Doo Hwan and eventually forced December's presidential election, South Korea's first in 16 years.

Police officials first maintained that Park had died of shock. When that story was met by disbelief, then-police chief Kang admitted that Park had been tortured to death and two low-ranking officers were charged. Six other officers eventually were implicated in the death and subsequent cover-up.

Kang was questioned at the time but was determined to have played no part in the cover-up. He resigned shortly after the incident.

But last week, on the anniversary of Park Chong Chul's death, the doctor who performed the autopsy implicated Kang in an alteration of the report.