One of 14 people, mainly Chinese nationals, sought over an alleged terror plot in Boston has been in US custody for two months, the FBI says.
The FBI still wants to locate the other named suspects
Mei Xia Dong, a Chinese woman, was initially identified as a man wanted in connection with an unspecified threat.
But the FBI said she had been traced to a border detention centre in the San Diego area and appeared to have entered the US for economic reasons.
The FBI said it was still interested in details on the other 13 on its list.
But it stressed that the apparent threat against Boston it received earlier in the month was "uncorroborated and of unknown reliability".
US TV networks reported on Wednesday that agents with radiological sensors were on patrol in Boston amid fears of a "dirty bomb".
Mei Xia Dong was on a list of 14 people the FBI said it wanted to question in connection with the threat.
But in a statement on its website on Saturday, the FBI said the woman had been traced to a US Customs and Border Protection detention facility in the San Diego area.
She had been there since being arrested for an alleged immigration violation on 11 November 2004.
"Investigation has determined that Mei Xia Dong paid an undisclosed sum to human smugglers to be brought into the United States from Mexico," the statement said.
"It appears at this time that Mei Xia Dong's motives for entering the US may have been for economic reasons. The investigation thus far does not tie her to any terrorist group."