Civil engineering senior Troy Grunder arrived at his first-floor Treehouse West apartment last month to find the door wide open. No one was there.

"You could tell somebody's been in there, messing with stuff," he said.

"Three computers were gone, my roommate's TV and DVD player were gone. They took my iPod."

A string of robberies in East Lansing apartment complexes might have been caused by a duplication or theft of a master key, East Lansing Police Lt. Kevin Daley said.

The robberies, which happened over the past couple months, have taken place in complexes owned by Cron Management, manager Julie Barrett said.

She said that although the company isn't missing any keys, it is in the process of changing the locks on all the apartment doors as a precaution.

"It does appear that someone had a key," she said.

"Before we had enough information, we decided to err on the side of caution. Our keys are not missing, but we don't have another explanation for it. We felt this was the way to make everyone feel more comfortable."

One man has been apprehended by police in connection to the robberies, and the department is seeking warrants for two more suspects believed to be involved with the thefts, Daley said.

The man in custody is being charged with four counts of home invasion.

Although police say there were between four and five break-ins, Barrett said she only knew of two and an attempted robbery.

The attempted robbery, at Treehouse West Apartments, 117 Center St., led to the arrest of a suspect last week.

"Someone knocked on their door, and the tenants didn't answer the door quickly," Barrett said.

"Then they started to let themselves in. The tenants called the police, and they responded very quickly. They caught him on foot."

Daley said an ex-employee of a subcontractor who worked with the complex didn't return the keys when released from the job.

"Ultimately, it went back to that individual, and the keys are in our possession," he said.

"What was very telling of (the robberies) was no forced entry. It was obvious from the initial report that they felt that this was possibly someone who had keys."

He said mostly small electronics were taken in the robberies, including computers and iPods.

Michelle Morley, a psychology sophomore and resident of Treehouse West, said she doesn't feel safe in her first-floor apartment.

"Bums come on my porch looking for bottles," she said, pointing out her glass sliding-door window to an open concrete patio.

Barrett said residents shouldn't be panicked.

"They don't have anything to worry about at all," she said.

"The locks have been changed, or the guy has been arrested, so there won't be an issue anyways."