DENTON — Two people were shot and killed and two others were wounded when gunfire erupted during a home invasion at a Denton student apartment complex Sunday evening.

"When we arrived, the officers determined that there was five individuals involved in some sort of altercation," said police spokesman, Officer Orlando Hinojosa.

A trail of blood and shell casings were found all along the first floor breezeway of Building 5. It's the chilling aftermath of what police say is a home invasion robbery inside an apartment.

Two men were dead at the Castle Rock Apartments in the 1500 block of Meadow Street, near Fort Worth Drive and I-35E. Two other men were taken to Denton Regional Medical Center for treatment. Hinojosa said the wounded are expected to survive.

Police believe there were three suspects and two victims. A fifth man is on the loose, and police say they aren't sure if he is injured. No names have been released.

In a rare twist, police say the two people killed may have been robbery suspects, shot by their victims.

Police said Monday three suspects forced their way into the apartment, where one suspect was shot and killed inside, then another suspect was shot and killed outside of Building 5.

The third suspect fled the scene and may be injured.

Neighbors heard fighting and shouting before shots rang out.

"I've never heard of anything happening right here like that, or that guns would go off right outside my window," David Risgbee said. "You know, not in a college area. It was scary."

Police say it's very unusual for anything like this to happen in Denton, let alone at an apartment complex filled with University of North Texas students. Many of them are home for winter break.

Police said the suspects and victims were not UNT students and are not from Denton. They said the relationship between the suspects and victims is unknown.

You can still see where a bullet pierced a neighbor's window. Another flew through their wall, landing just feet from where Cody Womack was sleeping.

"I's kind of life-changing," Womack said. "it kind of makes you think about things."

Neighbors stayed on lockdown for nearly 12 hours inside while police combed the area for evidence.

Two guns were recovered from the apartment. Police said one handgun belonged to the suspects and the other belonged to the victims.

Who shot who remains under investigation, Denton police said.

Apartment management didn't return News 8's requests for comment.

Denton has been hit by a rash of deadly crimes as 2014 draws to a close.

"We've had four in the last couple of weeks," Hinojosa said. "That's very unusual for the City of Denton. Towards the end of the year, that's unusual, especially during the Christmas holidays."