UC Davis officials announced Friday they've launched a criminal investigation into an explosion that rocked a campus apartment early Thursday morning.

The blast happened around 1:30 a.m. Thursday inside an apartment at the Russell Park complex on the west side of campus. The resident, a junior researcher employed by the university, suffered hand injuries and checked into Sutter Davis Hospital. The hospital then notified police.

When police arrived at the apartment, they found numerous chemicals and cordoned off the area, university spokesman Andy Fell said.

About 100 residents were ordered to evacuate, but were allowed to return Friday morning.

"This is now a criminal investigation based on the amount of items found inside the apartment," UC Davis Police Chief Matt Carmichael told reporters at a morning news conference.

Several agencies were called out to the scene, including the FBI; U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives; the Yolo County Narcotics Enforcement Team; and bomb squads from Sacramento, Placer and El Dorado counties.

Carmichael said some of the substances could not be safely transported, so authorities detonated the chemicals nearby in a series of eight explosions Thursday night. The police chief declined to say what chemicals were found, but noted it took 20 hours to remove the substances.

"It sounded like gunshots or fireworks," sophomore Daniel Connor said of the controlled detonations.

At the Friday news conference, Carmichael offered scant details about the researcher and the impending investigation.

He declined to release the individual's name or the department that employs him. He said so far no one has been charged or detained.

"It is important for us to maintain the integrity of the investigation," the police chief said, when pressed by reporters for more information.

Fell said that to his knowledge, "the researcher is still in the hospital."

Justin Aflatooni, a UC Davis senior who lives in the same building as the researcher, described him as a "very quiet guy who would wear shabby old polo shirts with khaki shorts."

He said a weird smell had circulated in the area before the explosion, but the researcher brushed it off, saying it was "burning toast."

Annaliese Franz, an assistant professor of chemistry at the university, said that without knowing what chemicals were being used, it would be "impossible" to speculate about the researcher's activities.

"There are many chemicals available in commercial locations, such as a grocery store," Franz said. "It doesn't require access to a chemistry department to obtain chemicals that can be potentially dangerous."

Law student Alex Monterrubio, who also lives in the building where the explosion occurred, said he heard the initial blast early Thursday.

"It was loud, but I didn't think too much of it," he said.

The researcher's apartment has been boarded up by police.

A homemade vent, presumably to dissipate fumes, had been installed in a front window.

Neighbor Sean Barberie said the vent had been there over a year.

"It wasn't suspicious," Barberie said. "I thought it was a vent for a dryer."

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