"It was like driving through a sea that opened in front of you and closed behind you."
He was with aid workers trying to pick up children who had lost their families, some of them in the exodus but many in horrific acts of genocide in their Rwandan homeland. They told him Hutu armed men would knock on Tutsi family doors and demand the man kill his wife or else they would come back and hack his mother, his wife and children to death and leave him to live with it.
"Anybody who was alive had seen some kind of murder," Seamus says.
Cholera was rampant in the camps and several times Seamus had to help pull traumatised children, mistaken for dead, out of pits where diseased and dismembered bodies were being dumped by the lorryload.
Wherever the aid truck stopped to collect lost children lots of adults climbed aboard to see if their child was there. Posting up lists of names did not help with mainly illiterate parents for whom it is taboo to mention the dead. But Seamus hit on the idea of using photographs. He persuaded Eastman Kodak to donate film and processing and with the help of UNICEF and the Red Cross began taking thousands of pictures of children that were pinned up with numbers for parents to scan.
Seamus fell ill and had to be flown home. But he returned and persuaded American photojournalist Tara Farrell to help him carry on. They took 21, 000 photos in a year - 60 to 80 per cent of these children found their family. Now his method of tracing is copied worldwide and a free travelling exhibition, supported by Eastman Kodak and Life magazine, is raising awareness about the effects of war.
Seamus, 31, describes Rwanda as "the most gruesome war there's ever been", but his work brought hope. He has since married Tara and their four-month-old girl's middle name is "Seka", Rwandan for "Smile".