More than one Hallifax crew is burried at oud Leusden. On the 22th June 1943 a canadian Hallifax BB375 EQ-T of 408 squadron crashed into the Lek. 2 Crewmembers survived, the others also are burried in Oud-Leusden. The wreck was salvaged in the '80ies. Another crashed on the 23th. At least 4 Hallifaxes crashed in that area around that date as far as I know.
Your cousin actually crashed in Zeist in a field between de Koelaan and the Kouwenhovenselaan at the same day (although some sources say it was on June 21th) time was around 2.45 and with the Krefeld ops being the major event that night with 700+ aircraft and at least 240 Hallifaxes, it seems likeley that your cousin had been participating in that action as well.