BANGKOK--A Thai police colonel known as “Jo Ferrari” due to his collection of fine cars, who was wanted on suspicion of involvement in the death of a detained drug dealer who was allegedly being shaken down for cash, turned himself in on Thursday amid a nationwide manhunt.

Police officials said Col. Thitisan Utthanaphon turned himself in at a police station in Saen Suk, a coastal village southeast of Bangkok. Another suspect, Lt. Thoranin Matwanna, was apprehended in a town southwest of the capital.

“I apologize that this has happened,” National Police Chief Suwat Janyodsuk told reporters at a news conference late Thursday. “We never release anyone who did wrong without punishment.”

He said little more about the case but gave the apprehended colonel an opportunity to address reporters by telephone and answer questions.

Thitisan defended his actions, denying any part in a shakedown and insisting he was attempting to get information from the drug dealer about where he had stashed his main supply of methamphetamine.

“Since I’ve been in the police I have never been involved in corruption,” the colonel said. “I did not have any intention to kill him. I just wanted to do my work.”

Thai media have reported that Thitisan had a collection of 29 luxury automobiles worth more than 100 million baht ($3 million), some of which he kept at a home in Bangkok worth about 60 million baht ($1.8 million).

One of the cars found at the house, a yellow Lamborghini, was purchased by Thitisan from a car company that was involved in a tax evasion investigation two years ago, the police Department of Special Investigation said. Thitisan was not charged in that case.

Police on Thursday did not immediately say what charges Thitisan is being held on.

Earlier in the day, five other suspects, including a major and a captain, were brought before a judge who ordered them held without bail on charges of dereliction of duty, torture and murder.

Thitisan, who was chief of the station in Nakhon Sawan province, disappeared shortly before a video surfaced on social media that appears to show him directing the deadly assault on the suspect.

Police started investigating the case only after a well-known lawyer, Decha Kittiwittayanan, published an account of it on his Facebook page on Sunday.

Decha said he had received a complaint from a junior policeman in Nakhon Sawan who said that police had arrested two drug suspects, the 24-year-old man and his female companion, with more than 100,000 methamphetamine tablets.

The policemen first demanded 1 million baht from the suspects, which they agreed to pay for their release, according to the account. But then Thitisan demanded double that amount and ordered his subordinates to cover the male suspect’s head with a plastic bag and beat him until he agreed, said the junior policeman, whose name was not revealed.

When the suspect died, Thitisan allegedly ordered his men to take the body to the hospital and tell the doctor the death was caused by a drug overdose. The junior policeman said the woman was released but told not to say anything about it, and that Thitisan paid the victim’s father to remain silent.

The initial police response to the furor over the story posted by the lawyer was to transfer Thitisan to another post.

On Tuesday, however, a video clip of the incident was shared on the Facebook page of another lawyer, Sittra Biabanggerd, who said he had received it from a police officer at the Nakhon Sawan station where all but one of the suspects worked.

It shows the male suspect in handcuffs being led into a room, his head covered with a black plastic bag.

He is then assaulted and thrown to the floor by officers who put more bags on his head. One of them appears to briefly kneel on him until he goes limp.

Allegations of police brutality and corruption are not uncommon in Thailand, and Human Rights Watch called Thursday for a transparent, outside investigation.

“A prosecution fully independent of the Thai police is needed if there is any hope of justice,” said Brad Adams, the group’s Asia director.

“Successive Thai governments have a long history of failing to ensure accountability for even the most ghastly police abuses against people in custody,” he said.