Another arrest was made in the investigation stemming from the abduction of a 6-year-old Nevada boy who was found during the weekend.

FBI spokeswoman Laura Eimiller said Monday that 42-year-old Terri Leavy was taken into custody by police Sunday in Fontana, Calif. Leavy is believed to be the companion of Clemons Fred Tinnemeyer, the grandfather of the boy, Cole Puffinburger.

Federal authorities said Leavy was wanted on an outstanding federal material witness warrant. U.S. Magistrate Oswald Parada late Monday ordered the pair detained without bond and turned over to the custody of the U.S. Marshals Service.

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The two will be taken to Las Vegas where they will remain in custody as material witnesses. Under a federal statute, they can be held for a "reasonable amount of time" until a deposition can be taken or they testify under oath. Leavy and Tinnemeyer have not been charged in the case.

Defense attorney Joan Politeo, who represents both material witnesses, declined to comment about the case.

Cole was set free late Saturday on a quiet Las Vegas street.

Authorities are looking into whether Tinnemeyer had ties to drug dealers. Police say he may have stolen millions of dollars from them.

Police have declined to elaborate on what role he played in the drug operation or whether the kidnappers had been seeking a ransom.

Messages left at a number believed to be for the Tinnemeyer home in Las Vegas were not returned.

Natalie Collins, a spokeswoman for the U.S. attorney's office in Las Vegas, said she could not release copies of the warrants and affidavits in the case because they were under seal.

Police said Monday they interviewed "several persons of interest" along with Cole about his nearly four days in captivity in hopes of gaining clues to the identity of gunmen who abducted him last week.

Two gunmen posed as police officers, bound his mother and her boyfriend, ransacked their home and kidnapped the boy Wednesday morning, authorities have said.

The boy was dropped off unharmed Saturday night in a residential neighborhood near downtown Las Vegas, and was found by a bus driver taking disabled passengers to their homes.

At a police news conference, bus driver Julio Diaz said his attention was drawn to a little boy wandering alone at 10:30 at night while he was driving his route.

"I saw this boy on the corner, I looked at the time and it got my attention that a boy like that would be ... wandering alone," Diaz said.

Diaz said Cole came to the bus and asked if Diaz could take him home. Diaz said he did not immediately recognize the boy as missing, but remembered thinking that "something was not right."

"He said he was left there. That's when I realized it was a police matter," Diaz said.

The driver took the blond, blue-eyed first-grader onto the bus and contacted police. The child said he had been dropped off just a few minutes before.

"The good thing, he wasn't shy about asking for help. I think he knew that he came to the right person," Diaz said.

Police Capt. Vincent Cannito called Diaz a "hero" in the case.

Police said Monday they believed the abductors were Mexican nationals involved in a methamphetamine ring, but said they could not be sure.

"We don't know who the suspects are at this point, so how can we say what nationality they are," police spokesman John Loretto said.

Police have said a third man also was involved.

Cannito said police have served "several" search warrants in different jurisdictions in their investigation of the kidnapping, but declined to be specific about what was found.

Cannito said police had "dozens of leads" and had interviewed numerous people, including several "persons of interest."

But Cannito said police were not ready to name any suspects in the case.

Cannito said authorities continued to search for Jesus Gastelum, a Mexican citizen whom Cannito said also used the name Ferdinand Gastelum.

Gastelum, who is in his mid-30s, is believed to be in Las Vegas or Southern California, police have said. Cannito declined to identify any of the other "persons of interest."

Cannito would not say whether another person of interest in police custody on Saturday had been released.

When Cole was found, "he was in good shape, he was extremely healthy, and he appeared to be very well cared for," Cannito said.

Cole was taken to University Medical Center as a precaution. He was examined and released to his father's care, hospital spokesman Rick Plummer said.

At an earlier news conference, the father, Robert Puffinburger, cried and thanked police and neighbors for helping to bring his son home.

"I'm just so glad he's safe," Robert Puffinburger said.

Neither police nor Cole's father would comment on Cole's mother or her father, a carpenter who filed for bankruptcy in 2001.

Click here for Adam Housley's "On the Scene" blog.