Authorities investigating the slaying of a family of four alongside a Florida highway said Friday that the father was probably involved in drug trafficking and that the suspected killer was in custody.

The suspect was among three men and a woman who were arrested Wednesday on drug charges and are "persons of interest" in the killings, Sheriff Ken Mascara said. None had been charged with the slayings, he said. Another man is being sought, he said.

The couple and their two young sons were found shot to death Oct. 13 off a desolate stretch of Florida's Turnpike near Port St. Lucie, about 50 miles north of their home in the Palm Beach County city of Greenacres.

Police searching the home after the killings found evidence that the father, Jose Luis Escobedo, was involved in drug trafficking, Drug Enforcement Administration agent David Weeks said in court papers filed Friday. The items were said to include "suspected drug ledgers" and plastic packaging used to wrap illegal drugs.

Investigators linked the drug suspects to Escobedo through references in the ledgers, among other things, the DEA agent said.

A search of the West Palm Beach home where three of the men under arrest were living turned up suspected crack, Ecstasy and drug packaging materials, the agent said. Investigators also found more than a dozen guns, including an AK-47 assault rifle. The DEA agent did not say if the weapons were used in the killings.

There also was a photograph of Escobedo with one of the suspects, Danny Varela, 26, according to court papers. The sheriff identified the other suspects as Liana Lopez, 18, Daniel Troya, 23, and Ricardo Sanchez, 23. The four were charged with possession of cocaine with intent to distribute.

The sheriff would not say which of the suspects is believed to have shot Escobedo, his 25-year-old wife, Yessica Guerrero Escobedo, and their sons, Luis Julian, 4, and Luis Damian, 3. But he told The Associated Press that it appeared those responsible for the killings were in custody.

"Indications are that there may be homicide charges filed," said Troya's lawyer, Ruben Garcia. "That's all I can tell you right now."

Lopez's attorney, Ronald Chapman, said he had just been assigned the case and wasn't prepared to comment. Messages left for the other suspects' attorneys were not immediately returned.

A fifth man, Juan Gutierrez, was arrested and charged in the drug case but is not named as a person of interest in the slayings. He told authorities he and Varela were at the Escobedos' home before the killings and helped destroy drug packaging materials, according to court papers.

Investigators believe the family's Jeep was pulled to the side of the highway and that someone inside the vehicle shot the family and drove away. Authorities have said the victims appeared to be lying down or kneeling when they were shot.

The Jeep was found abandoned in West Palm Beach three days later.

The family had moved to Florida in June from the Brownsville, Texas, area.

The sheriff said Escobedo's brother was involved in a heroin ring and is believed to be a fugitive in Mexico.