try to search here for the unit records:
http://www.44thbombgroup.com/main.html
here is list of all german claims known:
U.S.A.A.F. XII Bomber Command: WIENER NEUSTADT
01.10.43 Major Kurt Ubben: n.L. Stab III./JG 77 B-17
£ 14 Ost S/04 195: at 3.200 m. 11.55 Film C. 2031/II Anerk: Nr. -
01.10.43 Fw. Alfred Scharl: 6 2./JG 53 P-38
£ 15 km. S.W. Livorno: 4.000 m. 12.46 Film C. 2031/II Anerk: Nr.350
01.10.43 Oblt. Josef Jansen: 4 2./JG 27 B-24
£ E.N.E. Wiener Neustadt: 5.500-6.000 m. 12.55 Film C. 2031/II Anerk: Nr.19
01.10.43 Ltn. Gerhard Keppler: 7 2./JG 27 B-24
£ b. Wiener Neustadt: 5.500-6000 m. 12.57 Film C. 2031/II Anerk: Nr.19
01.10.43 Uffz. Hans Hambeck: 2 1./JG 27 B-24
£ S. Wiener Neustadt: 5.000 m. 12.59 Film C. 2031/II Anerk: Nr.162
01.10.43 Fw. Otto Haas: 2 1./JG 27 B-24 HSS
£ 20 km. S. Wiener Neustadt: 5.000 m. 13.05 Film C. 2031/II Anerk: Nr.170
01.10.43 Fw. Gustav Sturm: 1./JG 27 B-24 e.V.
£ S.S.W. Wiener Neustadt: 5.500 m. 13.05 Film C. 2031/II Anerk: Nr.170
01.10.43 Hptm. Hans Remmer: 19 1./JG 27 B-24
£ 35 km. S.S.W. Wiener Neustadt: 5.000 m. 13.06 Film C. 2031/II Anerk: Nr.166
01.10.43 Ltn. Emil Kaiser: 12 3./JG 27 B-24
£ 30-40 km. S. Wiener Neustadt: 4.500 m. 13.10 Film C. 2031/II Anerk: Nr.32
01.10.43 Ofw. Alfred Surau: 44 9./JG 3 B-17
£ 15 km. S.W. Feldkirch: 4.000 m. 13.33 Film C. 2031/II Anerk: Nr.838
01.10.43 Ltn. Stahlberg: n.L. 8./JG 3 B-17
£ 98 HT-6: 5.000 m. 13.35 Film C. 2031/II VNE:ASM
01.10.43 Ofw. Alfred Surau: 45 9./JG 3 B-17
£ Landquart: 3.700 m. (Switzerland) 13.40 Film C. 2031/II Anerk: Nr.839
01.10.43 Uffz. Meyer-Arend: n.L. 8./JG 3 B-17
£ 97 JU-4: 4.000 m. (N. Chur) 13.44 Film C. 2031/II Anerk: Nr.549
01.10.43 Uffz. Erich Kreul: 3 9./JG 3 B-17 HSS
£ 25 km. S.S.E. Feldkirch: 4.000 m. 13.45 Film C. 2031/II VNE:ASM
01.10.43 Ltn. Raimund Koch: 8 8./JG 3 B-17
£ JT-8: 4.500 m. (Ilanz 40 km. W. Chur) 13.47 Film C. 2031/II Anerk: Nr.559
Supplemental Claims from Other Sources:
01.10.43 Ltn. Horst Grimm: n.b 2./JG 27 B-24
£ S. Weiner Neustadt 13.00 Reference: JG 27 Lists f. 572
01.10.43 Ltn. Horst Grimm: n.b. 2./JG 27 B-24
£ Raum Weiner Neustadt 13.05 Reference: JG 27 Lists f. 572
01.10.43 Uffz. Franz Mörl: n.b. 2./JG 27 B-24
£ - - Reference: JG 27 Lists f. 572
01.10.43 Ltn. Emil Kaiser: n.b. 3./JG 27 B-24
£ Raum Weiner Neustadt 13.00 Reference: JG 27 Lists f. 572
01.10.43 Ofw. Rainer Pöttgen: n.b. 3./JG 27 B-24
£ - - Reference: JG 27 Lists f. 572
01.10.43 Uffz. Wolfgang Rentsch: 2 * 7./JG 3 B-17 HSS
£ - - Reference: JG 3 Lists f. 501
01.10.43 Oblt. Emil Bitsch: 105 8./JG 3 B-17
£ - 13.44 Reference: JG 3 Lists f. 501
01.10.43 Ltn. Raimund Koch: 9 8./JG 3 B-17 HSS
£ - - Reference: JG 3 Lists f. 501
Then you can try to pick up a group which might be involved. There are history books for all units written by Mr. Mombeek or Dr. Prien.
and try NARA, Washington and search for MACR, MIssion report and KU report related to the case of your fathers plane.
that is for the start. It is a puzzle and no one gives you complete answer.