(CNN) -- Police have executed a search warrant at the apartment complex where a missing Indiana University student lives, and authorities acknowledged Wednesday that they are becoming increasingly concerned about her safety.
"We believe that the chances are very great that there was foul play" in the disappearance of 20-year-old Lauren Spierer, Bloomington Police Department Lt. Bill Parker said at a news conference Wednesday morning.
Spierer was last seen around 4:30 a.m. Friday walking away from an apartment building at 11th and Morton streets in Bloomington, a few blocks from her home, after going to a bar with friends the night before. An acquaintance saw her walk toward the intersection of 11th Street and College Avenue, but police have said surveillance cameras at the Smallwood Plaza apartment complex, where she lives, do not show her arriving.
Parker said officers were looking for copies of security camera footage from that night when they broke through the doors at Smallwood Plaza Tuesday. He did not know why they were initially denied access, but he added that Smallwood personnel have been cooperative since. He explained that they obtained the search warrant because private businesses commonly want official paperwork before turning over evidence, and that was "perfectly normal."
In a statement provided to Bloomington's Herald-Times newspaper, a representative for the building's management said that nobody with a key was available on-site when police arrived to serve the warrant. According to the statement, "Smallwood Plaza has and will continue to fully support and cooperate with this police investigation, and respects the decision to obtain these hard drives as quickly as possible."
Parker said police have video of Spierer entering the apartment complex around 2:40 a.m. on Friday with a friend and then exiting 10 minutes later, although she did not go into her own apartment while she was there. They believe she and the friend then walked to the building at 11th and Morton, where other friends live.
Authorities are still examining the recordings, but Parker said, "We did not see indications on that video that she was being forced."
Police have interviewed many people, including Spierer's boyfriend and the friends she went out with the night she disappeared. They are also working on conducting polygraph exams. Investigators have obtained some evidence of value, but Parker would not specify what has been collected.
While anyone who was with Spierer on June 3 is considered a person of interest, Parker said, "We don't have anybody that we can characterize as a suspect."
Police and volunteer searches continued Wednesday. Parker said that a representative from the National Center for Missing and Exploited Children will assist in coordinating the searches.
"The entire city has been searched at least once" at this point, according to Parker, and some areas, particularly those close to Spierer's apartment building, have been looked at multiple times. Police now want to expand the searches beyond the city limits, although they do not have specific information indicating that Spierer was taken out of the city.
Spierer's father also spoke at Wednesday's news conference, again thanking the police and volunteers for all of their assistance.
"It's critical that we focus on finding Lauren," Robert Spierer said, noting that people from their hometown in Westchester County, New York, and others from around the country have come out to help with the searches.
"It's really hot out there. These people are incredible," he said of the volunteers. ROTC members in particular have been searching some difficult terrain, according to Spierer.
He again urged anyone with information related to his daughter to contact authorities, insisting that "nothing is too small, nothing is too insignificant."
Lauren Spierer is described as 4-foot-11 and approximately 95 pounds, with blond hair and blue eyes. When she disappeared, she was wearing black stretch pants, a tank top, a loose, light-colored shirt and no shoes.
Robert Spierer provided two numbers that people can call with tips: the Bloomington Police Department at 812-339-4477 and a tip line set up by America's Most Wanted at 800-CRIME-TV. All information can be provided anonymously.