LIMBE, Haiti (AP) _ When U.S. Special Forces pulled out of Limbe on the morning of Feb. 11, they believed local police were ready to assume control.

They were wrong. Only hours later, a mob stormed the police station and beat a Haitian lieutenant to death.

As U.S. forces prepare to hand over peacekeeping duties to the United Nations next month, the murder in this northern town symbolizes the fragility of Haitian security, despite a tailing off of political violence.

``We were in the process of weaning ourselves away from them,'' said U.S. Army Capt. Michael Stefanchik, based at Fort Bragg, N.C. ``We're going to have to start again, I guess.''

The Special Forces had been scaling back visits to Limbe, earlier considered one of the more stable towns in the area.

Now a dozen American soldiers are back in the police compound, which is ringed with high walls and barbed wire. They don't know when they're leaving.

Lakhdar Brahimi, head of the U.N. mission in Haiti, said the incident is isolated. ``These are not problems that prevent the country from moving ahead,'' he told The Associated Press.

Yet Haitian authorities remain heavily reliant on the U.S.-led multinational force, five months after it arrived to disband the armed forces and restore democracy after three years of military rule. President Jean-Bertrand Aristide returned to power Oct. 15.

At the peak of American assistance, there were 21,000 U.S. troops here. By the end of the month, there will be about 3,000 soldiers.

``It's going to take time to make the people understand they have to go through the steps of law,'' said Haitian police Maj. Charles Pierre, who is investigating the incident in Limbe, 80 miles north of the capital Port-au-Prince. ``They can't take measures by themselves.''

The victim was Lt. Antoine Henrys, one of two officers in the station the evening of Feb. 11. He was dragged outside, beaten and burned. His body was found buried in a shallow grave beside the river.

Authorities believe his killers were among eight members of a volunteer police corps who were angry at failing entrance exams for a new police academy.

But Haiti Progress, a leftist weekly newspaper, said the attack was likely a reaction against the ``recycling'' of the old military into the new police.

A big problem for Haiti's police force, which is being revamped, remains a lack of credibility. Many used to work for the old military, and are viewed as supporters of the old regime. The army and paramilitary thugs were believed responsible for killing as many as 4,000 people nationwide.

Most of Limbe's police left the town of 20,000 after Henrys' killing, fearing for their safety, and they appear unable to investigate on their own. On Friday, U.S. soldiers in body armor joined Haitian police from nearby Cap-Haitien in rounding up about 20 people for questioning.

``The Americans said, `We're looking for a guy with the same color T-shirt as you,' and they arrested me,'' said Franz Pierre, who was released later in the day along with most of the other suspects. Another man complained that soldiers forced open his door at 5 a.m. and subdued him with pepper gas.

After searching through warrens of tin and concrete shacks, authorities failed to find the volunteer police and a half-dozen M-1 rifles stolen from the station.

Even if the suspects are caught, there is no guarantee they will face justice. The local judge has closed his office because the town police force isn't operating. And so far, no eyewitnesses have come forward, fearing retaliation.

``There are people who know what happened but nobody's talking,'' said Superintendent Vernon Wilkinson, an international police monitor from Barbados.