Three Texans were arrested in Ohio last week after an investigation yielded evidence that they had attempted to mail a large quantity of fentanyl back to Texas, authorities said.

According to U.S. Attorney Justin Herdman of the Northern District of Ohio, it was enough fentanyl "to kill everyone in Toledo several times over."

One kilogram of the opioid was seized at a Toledo post office, and another half-kilo and $8,500 in cash were seized at a motel room where the trio were staying, the Toledo Blade reported.

The drugs had an estimated total street value of about $1 million, authorities said.

Fentanyl is “a dangerous synthetic opioid with deadly consequences for users and those in law enforcement,” Steve Francis, special agent in charge of the U.S. Immigration and Customs Enforcement homeland security investigations office in Detroit, told the Blade.

"The fentanyl seized is enough to kill everyone in Toledo several times over." — U.S. Attorney Justin Herman

The investigation began Monday after authorities learned that three "suspicious" people had checked in to two rooms at a Red Roof Inn in Toledo, the Dallas Morning News reported.

On Monday and Tuesday, police reportedly watched three individuals – identified as Darrius Lonzo Lewis, 29; Anthony Ray Robinson, 32; and Barbara Nykitta Wilson, 21 – leaving and entering the rooms.

Authorities said they watched Robinson and Wilson drive in separate cars to a post office Tuesday. Robinson reportedly entered the post office with a package, while Wilson returned a rental car before going back to the hotel in Robinson’s car, the Dallas Morning News reported.

After obtaining a search warrant, police found the drugs and cash and arested the suspects.

Further investigation led police to the post office, where authorities said they found a package containing more fentanyl.

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.

The trio were being held at the Lucas County Jail in Ohio, authorities said.