( CNN ) -- In an emotional open letter to the person responsible for her daughter 's disappearance , the mother of missing Indiana University student Lauren Spierer pledges to never give up searching for answers . `` If you think for a minute her father and I are going to disappear , think again , '' Charlene Spierer writes in the letter , written on the three-month anniversary of Lauren Spierer 's disappearance and released Saturday on the family 's `` Find Lauren '' web site . `` We are just as determined today as we were day one . You should know that Lauren is precious to us . ... We are in this for the long haul . Do you think we are going to walk away without finding out the answers ? Do you think we are going to rest until we find Lauren ? We will not . You have no idea who you have taken from us . We will never give up . '' Lauren Spierer , a 20-year-old sophomore , was last seen early June 3 after leaving a Bloomington , Indiana , sports bar with a male student . Surveillance camera footage from an alley between the two students ' apartment buildings showed them walking toward the male student 's building about 3 a.m. Spierer 's keys were later found in the alley , but she has not been seen since . One of the male student 's neighbors reported seeing Spierer leave about 4:30 a.m. , but police have said they found no sign of her after the 3 a.m. sighting on any of the surveillance video from the area between the two buildings . Police have not named any suspects.. In her letter , Charlene Spierer details the heartache her family has experienced since the disappearance . `` Much has happened over the past three months , '' she wrote . `` I wo n't bore you with the details , if you 've even gotten this far in reading this letter . I will say we have had the support and guidance of a multitude of people which has helped keep us going . For that generosity , we will be forever grateful . '' She recalls being asked by a young relative , at a birthday celebration for her other daughter , Rebecca , whether the family would celebrate Lauren Spierer 's birthday even if she was not there . `` I did n't really know what to say , '' she writes . `` Now I do . Of course we will celebrate Lauren 's birthday . '' She writes that as students returned to Indiana University for the fall semester , her family was packing her daughter 's possessions and shipping them home . `` Nineteen boxes , '' she said . `` Can you imagine that so much promise would fit into 19 boxes ? I wo n't go into the details of what it was like to pack Lauren 's things . I will just tell you it was excruciating . Every moment was excruciating . '' Charlene Spierer writes that she and her daughter share many things . `` Today I can add to that list , '' she says -- the day that marks three months since the disappearance is also Charlene Spierer 's birthday . She recalls feeling `` physically sick '' upon learning her daughter was missing , calling hospitals in the hope that a Lauren Spierer or Jane Doe had been admitted . She immediately flew to Bloomington from New York , she writes , and her father drove her to the airport . `` Imagine a grandfather , driving his daughter to the airport on the way to discover what has happened to his granddaughter , '' she writes . `` Imagine that . There were few words exchanged . There are no words . '' `` You are responsible for Lauren 's disappearance , '' she writes . `` You know where she is . You are guilty of a heinous crime . '' She closes by asking the person , `` What are you thinking ? I would really like to know . I am waiting to hear from you . '' At the end , she attaches a brief note to her daughter : `` Dearest Lauren , we are loving you . Missing you . Always , Mom . '' Lauren Spierer was last seen wearing black pants and a white tank top with a white shirt , according to her family 's web site . She is 4 feet 11 inches tall and weighs 95 pounds and has blond hair and blue eyes . Police searched a landfill outside of Bloomington last month in connection with Spierer 's disappearance . Nothing was found , according to CNN affiliate WISH . Attempts to reach the Spierer family Sunday were not immediately successful .
Lauren Spierer was last seen on June 3 . Her mother writes a letter to the person responsible for the disappearance . `` You are guilty of a heinous crime , '' she writes . The letter is addressed to an unknown person, and it says that her daughter has been missing since July 4.