Three Houston-area residents were arrested in Ohio this week after federal authorities say they attempted to mail the synthetic opioid fentanyl back to Texas.

According to a criminal complaint, authorities started monitoring a Red Roof Inn in Toledo on Monday after the hotel staff reported that three suspicious people had checked into two rooms.

Law-enforcement officers reported watching as Darrius Lonzo Lewis, 29, Anthony Ray Robinson, 32, and Barbara Nykitta Wilson, 21, came and went from both rooms that day and the next.

From left: Darrius Lonzo Lewis, Anthony Ray Robinson, Barbara Nykitta Wilson (Lucas County Sheriff's Office)

On Tuesday, authorities said, Robinson and Wilson left the hotel in separate cars and met up at a post office. Robinson went into the post office with a package while Wilson returned her rental car, then Robinson picked her up and they went back to the hotel.

Officers got a search warrant for the box Robinson had dropped off and found about 1 kilogram of fentanyl inside, wrapped in heat-sealed plastic bags and packed in coffee grounds in an apparent attempt to avoid detection.

Authorities later searched the Red Roof Inn rooms, where they found more than $8,000 and about half a kilogram of fentanyl.

"The fentanyl seized [on Tuesday] is enough to kill everyone in Toledo several times over," U.S. Attorney Justin Herdman said in a statement.

When investigators questioned the trio, the complaint says, Robinson and Wilson said they were half-siblings who had driven up from Texas — for a wedding, according to Robinson, and for a proposal dinner by Wilson's account. Lewis said he had flown to Ohio from Houston.

Robinson reportedly denied knowing Lewis, while Wilson said he was her half-brother's best friend. Lewis told authorities he didn't know Robinson but was going to drive back to Texas with Wilson.

Authorities arrested all three, and they remained in the Lucas County jail Friday.

Court records show that Lewis and Robinson each have been convicted of a number of crimes in Harris County, including drug- and weapons-related offenses. Wilson has been convicted of theft.

According to the federal Centers for Disease Control and Prevention, Ohio's drug overdose mortality rate in 2016 — the most recent year for which the data is available — was second in the nation behind West Virginia's. Last year, the Department of Health and Human Services declared the opioid epidemic a national crisis.

"Individuals from out of state who think they can come into Ohio to traffic drugs undetected should know that we have task forces like this one across the state whose mission is to find you, seize your drugs, and stop you from profiting off of Ohioans who are suffering from addiction," Ohio's attorney general, Mike DeWine said in a statement.