( CNN ) -- Our youngest child , Peter , was murdered on September 11 , 2001 , while attending a conference at Windows on the World at the World Trade Center . He was 25 years old when he died . When the towers fell , we were in France , on vacation to celebrate Steve 's 60th birthday . Peter , our daughter , Jane , and our son Jeff and his wife , Tobey , had all been with us for a week before flying back to the U.S. on September 8 . On the day of the attacks , we were terribly upset after hearing the news . But at first , we were not worried about our kids . Jeff and Tobey lived in Tulsa . Jane lived in D.C. but her job was nowhere near the Pentagon . Peter worked in midtown Manhattan for Bloomberg LP . But since he traveled throughout the city for his job , we became concerned . We desperately tried calling our kids but could not get a line out of France . It was n't until late in the day that we learned from Jeff that `` Pete was there . '' The next day , Michael Bloomberg , who became mayor two months later , called to tell us that Pete was dead . My world stopped , and it still is totally out of kilter . News : Triple-amputee veteran gets 'smart ' home on September 11 . Not Peter ! Pete was all laughter and sunshine and love . He was n't uncomfortable kissing his mother or father in public , or hugging his sister for no reason at all . He and Jeff traveled to fun places and laughed and laughed . Not Peter -- he was too full of life . Our mark on this Earth is our children . After his death , we knew we had to leave a mark that Peter existed and the world would be a better place because he lived . In searching for a way to honor his life , we learned that 1 billion people , almost one sixth of humanity , have directly experienced torture , terrorism or mass violence . Victims are left with lifelong emotional wounds preventing them from leading productive lives . In sub-Saharan Africa , the incidence of traumatic depression and PTSD exceeds that of HIV/AIDS , malaria and TB combined . Peter loved life ; he was compassionate and caring . There was nothing we could do for Pete , but returning survivors to life in his name was the perfect memorial . In March 2003 , we created the Peter C. Alderman Foundation . People often ask : `` Why are you dealing with traumatic depression and PTSD when there are so many greater problems in the world ? '' Our response is simple : Billions of philanthropic dollars go into fighting HIV/AIDS , malaria and poverty . But if people do n't care whether they live or die , they will not follow through with their medication regimens , walk that extra mile for potable water or take advantage of microfinance . If you can restore hope , a person is less likely to strap on dynamite and kill innocent people . Opinion : 11 years after 9/11 : Who are the terrorists ? Our foundation started by training indigenous health workers , but we quickly learned that training by itself was not sufficient . We needed to provide a framework in which professionals could work . To that end , our foundation runs eight trauma clinics in Cambodia , Uganda , Liberia and Kenya . Establishing public-private partnerships with local governments , our foundation trains , supervises and pays its staff ; the government provides clinic space , in-patient beds and psychotropic drugs . Our foundation 's average annual cost per clinic is $ 30,000 . More than 30,000 children have been abducted in Uganda , and many of our patients are child soldiers , like Patrick . He has been treated in our Kitgum clinic for two years . Now he no longer has nightmares or flashbacks . He can sleep through the night and hold down a job . He no longer thinks of suicide . He has even named his new baby after his counselor at the clinic . Our foundation sponsors an annual African training conference on traumatic depression . Watch : The Alderman 's talk to CNNMoney . At July 's fifth annual conference in Tanzania , attended by 500 mental health professionals from 22 countries , an imam from Somalia rose to say the opening prayer . He only spoke Arabic . When translated , we learned that he had said a prayer for Peter . Tears streamed down my face as I realized we were truly on the way to leaving that mark for Peter . The work has kept us functioning and given us a reason to get out of bed every day . Nothing can erase our pain , but our passion to leave a profound and indelible mark that Peter existed on this Earth has propelled us forward . Peter would be very proud of the foundation that bears his name . The opinions expressed in this commentary are solely those of Elizabeth Alderman and Stephen Alderman .
Elizabeth and Stephen Alderman : Our youngest son , Peter , was killed on 9/11 . After his death , they knew they had to leave a mark that Peter existed . They set up the Peter C. Alderman Foundation to help people affected by terrorism . Elizabeth , Stephen Alderman : Peter would be proud of the work that bears his name .