Updated

Preliminary chrages have been filed against a French nuclear scientist described by colleagues as a well-regarded "loner" for "criminal association with a terrorist enterprise," according to French judicial officials.

An Algerian-born French citizen, who has been identified by various news outlets as 32-year-old Adlene Hicheur, was arrested last week over suspected links to the North African branch of Al Qaeda, which seeks to install an Islamic state in Algeria.

Hicheur, who was tracked for 18 months by French counterterrorism officials before his arrest in France Thursday, received his doctoral training at Stanford University and worked on the Large Hadron Collider, the world's largest atom smasher, at a facility in Switzerland.

Under French law, filing preliminary charges gives the investigator time to pursue the inquiry before deciding whether to send a suspect for trial or drop the case.

French judicial officials say Hicheur has acknowledged that he corresponded online with Al Qaeda in the Islamic Maghreb and vaguely discussed plans for terror attacks. He has not been charged with planning an attack.

A spokesman for the research center in Switzerland where Hicheur was working on the Large Hadron Collider described Hicheur as “quiet, conscientious and well-regarded,” and asserted that he did not have access to sensitive material.

While there are small amounts of radioactive materials on the CERN site, Hicheur did not have “access or security clearance” for highly-sensitive “experimental areas,” spokesman James Gillies told FOX News.

Gillies said that CERN does not have material or equipment on site that would be “useful in a terror attack,” and he said there are “no indications” CERN was itself a target for a terrorist strike. Hicheur worked in a laboratory to understand phenomena such as anti-matter and the Big Bang theory on the origin of the universe.

"There's nothing in there that people can steal and use for terrorist ends, nothing at all. It's all about personal safety," Gillies said. "There are areas where we have cryogenic liquids, high magnetic fields, particle beams and so on, where you need specialist knowledge to be able to go there," Gillies said.

Hicheur was one of more than 7,000 scientists working at the facility, which straddles the border between France and Switzerland. Gillies would not say whether background checks are conducted on the scientists working there.

"This guy has a doctorate in particle physics, so he's clearly an intelligent person. It does take some intelligence, it does take some dedication to achieve qualifications at that level," he said.

Colleagues at the Federal Polytechnic Institute in Lausanne, Switzerland, where Hicheur also worked, expressed their astonishment at his arrest.

"We are pretty shocked and surprised," said Jerome Grosse, spokesman for the institute, where Hicheur worked as an instructor in experimental physics.

He said the institute had “no idea” there could be questions about Hicheur’s past, and his colleagues remembered him as a “serious" man and a "hard worker” — but one who remained a “loner.”

Grosse said Hicheur had not been seen at work for most of the year because he was ill, but he had been in touch with the institute via e-mail.

The Associated Press contributed to this report.