AYER — Police are investigating an “unusual” home invasion that took place at a Willard Street apartment.

Three unarmed Caucasian males reportedly forced their way into a young woman’s apartment July 21 at approximately 2 a.m. and demanded valuables from its occupants, said police Chief Richard Rizzo, but the perpetrators fled empty-handed after the tenant called 911.

No serious injuries were reported, he said, and no arrests have been made as of yet.

The tenant, Samantha Warwick, 26, told police she’s acquainted with two of the perpetrators, who live in Fitchburg, said Rizzo. The third man — described as a rugged six-foot Hispanic individual — has not yet been located.

“We’re seeking warrants on two of the suspects, and the third guy we haven’t identified yet,” said Rizzo.

Warwick couldn’t be reached for comment.

The entire incident took less than five minutes, said Rizzo. Statements given to police indicate Warwick opened her apartment door slightly after someone knocked, and the trio of perpetrators forced entry from there. Warwick had two young men in the building with her, one of whom was held against the wall by the Hispanic man during the incident.

The perpetrators reportedly demanded a computer game system they thought was in the house and rifled through the wallet of one of the young men. They also searched the apartment for anything of value.

While the thieves were thus occupied, Warwick called 911 with her cell phone, but was discovered and had the phone slapped out of her hand. She then ran into another room to use a different phone, but was allegedly thrown to the ground and punched several times by one of the intruders.

The crooks left shortly after, but smashed a glass coffee table and punched one of the young men in the head before leaving.

Afterward, the victims didn’t speculate on the robbers’ motivation, said Rizzo.

“They claimed they didn’t know,” he said.

Likely charges include unarmed assault with the intent of robbing, unarmed assault and burglary, and the destruction of less than $250 of property. Rizzo said the charges were all listed as misdemeanors, which carry a maximum sentence of less than two years.

Overall, he termed the incident curious and still under investigation.

“It’s unusual,” he said. “Usually when people push in a door to a property like this, there’s more to it than what the victims are saying. It’s still under investigation.”